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ICRP ref 4819-7515-1888
2012 July 03

Annals of the ICRPICRP Publication XXX

Assessment of Radiation Exposure of Astronautsin Space
Editor
C.H. CLEMENT
Assistant Editor
M. SASAKI
Authors
G. Dietze, D.T. Bartlett, F.A. Cucinotta, M. Pelliccioni, T. Sato, V. Petrov,
G. Reitz, I.R. McAulay, J. Xianghong, D.A. Cool

PUBLISHED FOR
The International Commission on Radiological Protection

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TITLE PAGE……………....................................................................................

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GUEST EDITORIAL.........................................................................................

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ABSTRACT.......................................................................................................

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PREFACE.......................................................................................................................

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MAIN POINTS...............................................................................................................

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EXECUTIVE SUMMARY............................................................................................

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GLOSSARY...................................................................................................................

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1. INTRODUCTION....................................................................................................

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2. RADIATION ENVIRONMENT IN SPACE. .........................................................
2.1
Primary radiation field........................................................................................
2.2
Galactic cosmic radiation...................................................................................
2.3
Solar cosmic radiation........................................................................................
2.4
Trapped radiation................................................................................................
2.5
Interaction with magnetic fields.........................................................................

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3. QUANTITIES USED IN RADIOLOGICAL PROTECTION.................................
3.1
Dose quantities in radiological protection..........................................................
3.1.1 Protection quantities............................................................................................
3.1.2 Operational dose quantities.................................................................................
3.2
Description of radiation quality...........................................................................
3.2.1 Relative biological effectiveness.........................................................................
3.2.2 Radiation weighting factor..................................................................................
3.2.3 Quality factor.......................................................................................................
3.3
Approach for space applications..........................................................................
3.3.1 Protection quantities.............................................................................................
3.3.2 Quantities for measurements................................................................................
3.3.3 Quantities for high doses......................................................................................

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4. METHODS OF MEASUREMENT OF RADIATION FLUENCES
AND DOSES............................................................................................................
4.1
Measurement quantities......................................................................................
4.2
Purpose of Measurements......................................................
4.3
Instrumentation for radiation spectrometry, area and individual monitoring......
4.3.1 General.................................................................................................................
4.3.2 Active devices.......................................................................................................
4.3.3 Passive devices.....................................................................................................
4.4
Biomarkers of exposure.......................................................................................
4.5
Instrument characterisation and calibration.........................................................
4.6
Accuracy and uncertainties for measurements in spacecraft................................

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5. RADIATION FIELDS INSIDE SPACECRAFT AND ON

CONTENTS

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PLANETARY SURFACES......................................................................................
5.1
General................................................................................................................
5.2
Physics of space radiation transport...................................................................
5.2.1 Radiation transport..............................................................................................
5.2.2 Atomic processes................................................................................................
5.2.3 Nuclear interactions............................................................................................
5.3
Proton, neutron and heavy ion transport codes...................................................
5.3.1 Inter-comparison and validation of radiation transport codes.............................
5.4
Radiation fields inside spacecraft........................................................................
5.5
Radiation shielding..............................................................................................
5.6
Lunar and Mars surface.......................................................................................

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6. RADIATION FIELDS AND DOSES IN THE HUMAN BODY.............................
6.1
Phantoms..............................................................................................................
6.2
Dose conversion coefficients...............................................................................
6.3
Calculation of organ doses of astronauts within spacecraft..............................
6.4
Assessment of doses in the body by measurements............................................
6.5
Biodosimetric measurements..............................................................................

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7. OPERATIONAL RADIATION PROTECTION IN SPACE....................................
7.1
Pre-flight mission design.....................................................................................
7.2
Area monitoring...................................................................................................
7.3
Individual monitoring..........................................................................................
7.4
Dose recording.....................................................................................................
7.5
Consideration of uncertainties.............................................................................

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8. CONCLUSIONS.......................................................................................................

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REFERENCES................................................................................................................

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ANNEX
Conversion coefficients and mean quality factors for protons, neutrons,
alpha particles and heavy ions (2 < Z ≤ 28).

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PREFACESpace flight is one of the occupational exposures from natural sources already listed in
ICRP Publication 60 (1991), but the number of persons involved in space flights was smalland hence no guidelines have been developed by ICRP to date.
The present report is the first publication of the International Commission on
Radiological Protection (ICRP) dealing with the topic of radiation exposures of astronauts inspace. The following terms of reference were given to the Task Group preparing this report:
 Analyze the radiation fields in space with special attention to the high-LET components
and solar particle events,
 Investigate the application of dose quantities used in radiological protection , Describe devices for measurement of particle fluences and doses in space environment, Describe procedures of the assessment of doses to astronauts performed bymeasurements and calculations, and Present some data of fluence-to-dose conversion coefficients for heavy ions.
The report was prepared by a Task Group on “Radiation Protection in Space” of ICRP
Committee 2. The membership of the Task Group was:G. Dietze (Chairman)
M. Pelliccioni
T. Sato

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D.T. Bartlett
V. Petrov

Corresponding members were:
I.R. McAulay
D.A. Cool
J. Xianghong

F.A. Cucinotta
G. Reitz

J. Cooper

The membership of Committee 2 during the preparation of this report was:(2005-2009)
H.G Menzel. (Chairman)
W. Bolch
A. BouvilleV. Berkovski
N. Ishigure
K. Eckerman
N. Ishigure
J. Lipsztein
H. Paretzke
A. Pradhan
Ch. Streffer (Chairman until 2007)(since 2009)
H.G Menzel. (Chairman)
D. Bartlett
G. Dietze
J. Harrison
R. Leggett
N. Petoussi-Henss

M. Balonov
G. Dietze
J. Harrison
F. Paquet
J. Stather
Z. Yongzeng

W. Bolch
V. Berkovski
K. Eckerman
Jinzeng Ma
J. Lipsztein
A. Pradhan

M. Balonov
R. CoxA. EndoN. Ishigure
F. Paquet

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MAIN POINTS The radiation field astronauts are exposed to in space is very complex. It contains
electrons, protons, alpha particles and heavier ions up to very high energies fromgalactic cosmic radiation, protons and electrons emitted from the Sun, protons andelectrons trapped in belts by the magnetic field of the Earth, and various secondary
radiations created in interactions of the primary radiation with materials of thespacecraft. Depending on the time present in space, mission doses to astronauts may
become much higher than 100 mSv. Only external radiation exposure to astronauts
needs to be considered.
 Due to the specifics of the radiation field in space not all concepts of quantities
defined for radiological protection applications on Earth are appropriate forapplications in space missions, especially when risk assessment is an important task.
A radiation weighting factor wR = 20 for all types and energies of heavy ions in thedefinition of equivalent dose is not justified. For heavy ions the ratio of wR and meanquality factors averaged over the human body is up to a factor of 10 depending on thetype and energy of the ion.
 No specific operational dose quantity is recommended for area monitoring in space.
Quantities to be measured are radiation fluence rates and energy distributions ofdifferent types of particles, and LET-distributions. For individual monitoring,measurement of absorbed dose at the surface of the body in combination with LETdistributions may be appropriate for an assessment of effective dose equivalent ororgan dose equivalent.
 Radiation transport calculations are important tools for information about radiation
exposure of astronauts. Based on data about the primary radiation fields transport
calculations are able to calculate radiation fields inside spacecrafts, fields on the bodyof astronauts and in organs or tissues of anthropomorphic phantoms.
 Generally, two different procedures may be applied for the assessment of doses in theastronaut´s body by calculations. One may either assess the radiation field parametersnear to an astronaut and then apply fluence-to-dose conversion coefficients for all
types of particles involved for the assessment of organ doses or one may calculateorgan doses in a body using the radiation field data outside of the spacecraft and acode which combines radiation transport in the spacecraft and in the human body.
Measurements with individual dosemeters near to the body of an astronaut incombination with calculations may be directly correlated to doses in the human body.
 The report presents conversion coefficients for mean absorbed doses in organs andtissues of the body for heavy ions up to Z = 28. The calculations are based on thereference voxel phantoms following the 2007 Recommendations of the Commission.
Data are given for isotropic (ISO) exposure of the body. Also mean quality factors,
QT, for the specified organs and tissues of the body are presented. QT-values vary
between about 2 and 25.
 Information and data are also presented for the quality factor concept derived from thetrack structure of charged particles in tissue as proposed by NASA... This results in adifferent distribution of Q in terms of LET with a stronger decrease of Q withincreasing LET.

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EXECUTIVE SUMMARYa) Astronauts are living and working in low Earth orbits for extended periods of time,
especially during the operation and maintenance of the International Space Station (ISS) andscientific investigations. Furthermore, plans are already discussed for outer space missions ofastronauts.
b) . In ICRP 103 it is stated that “in exceptional cases of cosmic radiation exposures, suchas exposure in space travel, where doses may be signiﬁcant and some type of control
warranted, should be dealt with separately from the conventional approach of occupational
exposure”. Therefore, although astronauts are exposed to ionizing radiation during theiroccupational activities they are usually not classified as being occupationally exposed in thesense of the ICRP system for radiation protection.
c) The report contains 7 Chapters. The first one is an introduction describing the specificsituation of astronauts in space and the differences of the radiation field in space compared tofields on Earth, thereby showing areas where approaches applied in radiological protection
measures on Earth need to be modified.
d) In Chapter 2 the radiation fields in space are described in detail. The solar system with
the Sun at its centre is embedded in a complex mixture of galactic cosmic radiation (GCR) protons, -particles and heavy ions - which continuously enters the heliosphere from all
directions. Inside the heliosphere, the GCR fluence rate and particle energy distributions are
modulated by the interplanetary magnetic field produced by the charged particles
continuously emitted by the Sun, the so-called solar wind. In addition to the solar wind, theSun occasionally emits unusually large pulses of energetic particles – mostly protons andelectrons – called solar-particle events (SPEs). Celestial bodies equipped with a magnetic
moment like the Earth are surrounded by toroidal belts of particulate radiation. Such radiation
belts constitute an important third primary exposure source. Fluence rates of cosmic radiation
are not constant; they vary between two extremes which correspond in time with the
maximum and minimum solar activity. Solar activity and cosmic radiation fluence rates areinversely correlated. In Sections 2.2 to 2.5 the various components of the radiation field inspace are presented and the influence of the Earth´s magnetic field is described.
e) Chapter 3 is dealing with the quantities used in radiological protection. In the first partthe system of dose quantities as given in Publication 103 (2007) is described and secondly the
relative biological effectiveness (RBE) is discussed especially with respect to the large
contribution of heavy ions and the very high energies. A single wR-value of 20 for all heavy
ions of all energies is not appropriate for space radiation fields. Hence, for space applications
the concept of a quality factor, Q(L), is applied also to the protection quantities. In Section
3.3 the approach for applications in space is described in detail.
f) In Chapter 4 the methods of fluence and dose measurements in space are described.
This includes instrumentation for fluence measurements, radiation spectrometry, area
dosimetry, and individual monitoring. Passive and active devices are mentioned and also theuse of biomarkers for the assessment of mission doses is described. Some advice for quality
control and the assessment of uncertainties is also given in this Chapter.
g) In Chapter 5 the methods of determining quantities describing the radiation fields
within a spacecraft are given. Radiation transport calculations are the most important tool foran assessment of radiation fields inside a spacecraft starting from the radiation field in freespace and considering the walls and further equipment of the spacecraft. In this chapter some6

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physical data used in radiation transport codes are presented and the various codes used for
calculations in high-energy radiation fields as in space described. Results of calculations ofradiation fields in spacecrafts are given. A discussion of shielding possibilities is included inthis Chapter, too.
h) Chapter 6 is dealing with methods of determining mean absorbed doses and dose
equivalent s in organs and tissues of the human body. Calculated conversion coefficients offluence to mean absorbed dose in an organ or tissue are given for heavy ions up to Z=58 forenergies from 10 MeV/u to 100 GeV/u. For the same set of ions and ion energies meanquality factors in organs and tissues are presented using on the one hand the Q(L) function
defined in Publication 60 of the Commission and on the other hand a Q(Z,E) function
proposed by NASA. In Sections 6.4 assessment of doses in the body by measurements aredescribed and results are compared with calculations. In Section 6.5 biodosimetricmeasurements for the assessment of mission doses are presented.
i) In Chapter 7 operational measures with regard to the assessment of the exposure ofastronauts during space missions. This includes pre-flight mission design, area and individual
monitoring during flights in space and dose recording. The importance of considering
uncertainties in dose assessment is also mentioned.
j) In an Annex numerical data of conversion coefficients and mean quality factors for
protons, neutrons, alpha particles and heavy ions (2 < Z ≤ 28) are given.

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GLOSSARY

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Absorbed dose, D

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The absorbed dose is the quotient of d  by dm:

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D

d
dm

where d  is the mean energy imparted by ionising radiation to matter of mass dm. The unitof absorbed dose is joule per kilogram (J/kg), and its special name is gray (Gy).
Ambient dose equivalent, H*(10)The dose equivalent at a point in a radiation field that would be produced by thecorresponding expanded and aligned field in the ICRU sphere at depth of 10 mm on theradius vector opposing the direction of the aligned field. The unit of ambient dose equivalent
is joule per kilogram (J/kg), and its special name is sievert (Sv).
Biomarker
A traceable substance indicating changes in a cell or an organ caused by environmental
actions, e.g. by ionising radiation.
Charged Particle Equilibrium
Charged particles equilibrium in a volume of interest means that the energies, numbers anddirections of the charged particles are constant throughout this volume. This is equivalent tosaying that the distribution of charged particle energy radiance does not vary within thevolume. In particular, it follows that the sums of the energies (excluding rest energies) of thecharged particle entering and leaving the volume are equal
Cross section, The cross section of a target entity for a particular interaction produced by incident charged
or uncharged particles of a given type and energy is given by:



N
Φ

where N is the mean number of such interactions per target entity subjected to the particle
fluence, Φ. The unit of cross section is m2. A special unit often used for the cross section isthe barn where 1 barn (b) = 10-28 m2. A full description of an interaction process requires,inter alia, the knowledge of the distributions of cross sections in terms of energy anddirection of all emergent particles from the interaction. Such distributions, sometimes called’differential cross sections’, are obtained by differentiations of  with respect to energy andsolid angle.
Deterministic effectSee ‘Tissue reaction’.
Detriment
The total harm to health experienced by an exposed group and its descendants as a result of
the group’s exposure to a radiation source. Detriment is a multi-dimensional concept; its
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principal components are the stochastic quantities probability of attributable fatal cancer,
weighted probability of attributable non-fatal cancer, weighted probability of severe heritableeffects, and length of life lost if the harm occurs.
Directional dose equivalent, H´(d,The dose equivalent at a point in a radiation field that would be produced by thecorresponding expanded field in the ICRU sphere at a depth, d, on a radius in a specified
direction, . The unit of directional dose equivalent is joule per kilogram (J/kg) and its
special name is sievert (Sv).
Dose conversion coefficient
A coefficient relating a dose quantity to a physical quantity, both for internal and externalradiation exposure. In internal dosimetry this term is also called a ’dose coefficient’.
Dose equivalent, H
The dose equivalent at a point in tissue is given by:
H=QD
where D is the absorbed dose and Q is the quality factor at that point. The unit of dose
equivalent is joule per kilogram (J/kg), and its special name is sievert (Sv).
Dose equivalent in an organ or tissue, HT,Q
The product of the mean quality factor, QT, and the mean absorbed dose, DT, in an organ or
tissue T:
HT,Q = QT DT .
A quantity introduced by ICRP in Publication 26 and replaced by equivalent dose in an organor tissue in Publication 60.

Dose limit
Recommended value of a dose to an individual that shall not be exceeded in planned
exposure situations.
Effective charge number, Z*
The charge number Z of a nuclei reduced by a factor depending on the relative velocity (velocity of the nuclei relative to the velocity of light) which takes account of the fact that at
low velocities the nuclei is not completely ionised. It is
Z* = Z (1-exp(-125  Z2/3))
Effective dose, E
The tissue-weighted sum of equivalent dose in an organ or tissue from all specified organs
and tissues of the body, given by the expression:E   wT  wR DT, R   wT H T
T

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R

T

where HT is the equivalent dose in an organ or tissue T, DT,R is the mean absorbed dose in an
organ or tissue T from radiation of type R, and wT is the tissue weighting factor. The sum isperformed over organs and tissues considered to be sensitive to the induction of stochastic

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effects. The unit of effective dose is joule per kilogram (J/kg), and its special name is sievert(Sv).
Effective dose equivalent, HE
The tissue-weighted sum of dose equivalent in an organ or tissue from all specified organs
and tissues of the body, given by the expression:
H E   wT H T, Q
T

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where HT,Q is the dose equivalent in an organ or tissue T. The unit of effective dose
equivalent is joule per kilogram (J/kg), and its special name is sievert (Sv).
A quantity introduced by ICRP in Publication 26 and replaced by effective dose in
Publication 60.
Equivalent dose in an organ or tissue, HT
The equivalent dose in an organ or tissue is given by:
H T   wR DT, R
R

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where DT,R is the mean absorbed dose from radiation of type R in the specified organ or
tissue T, and wR is the radiation weighting factor. The unit of equivalent dose is joule perkilogram (J/kg) and its special name is sievert (Sv).
Fluence, The quotient of dN by da, where dN is the number of particles incident on a sphere of crosssectional area da, thus:
Φ

dN
da

The unit of fluence is m-2.
Galactic cosmic radiation (GCR)
Charged particle radiation which continuously enters the heliosphere from outer space fromall directions. The radiation contains electrons (about 2%) and a broad range of charged
particles from protons up to high-Z particles with high energies up to several hundreds of
GeV and even higher. The fluence rate of the GCR in the heliosphere is inversely correlatedwith the solar activity. It is caused by the solar magnetic field, which is coupled to the solar
wind.
Geomagnetic cut-off rigidity
See “rigidity threshold”.
Heavy ion
Ions of elements heavier than He.
Heliosphere
The space formed by the Sun and its planets.

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ICRU 4-element tissue
ICRU 4-element tissue has a density of 1 g/cm3, and a mass composition of 76.2 % oxygen,
11.1 % carbon, 10.1 % hydrogen, and 2.6 % nitrogen.
ICRU sphereA hypothetical sphere, 30 cm in diameter, of tissue-equivalent material (ICRU 4-element
tissue) with a density of 1 g cm-3 and a mass composition of 76.2 % oxygen, 11.1 % carbon,
10.1% hydrogen and 2.6 % nitrogen.
K-, Kp-index
Index quantifying disturbances in the horizontal component of Earth's magnetic field with anumber in the range 0-9 with 1 being calm and 5 or more indicating a geomagnetic storm.
The K-index is derived from the maximum fluctuations of horizontal components observed
on a magnetometer during a three-hour interval. The official planetary Kp-index is derived by
calculating a weighted average of K-indices from a network of geomagnetic observatories.
Kerma, K
Quantity for ionising uncharged particles, defined by the quotient of dEtr by dm, where dEtr
is the mean sum of the initial kinetic energies of all the charged particles liberated in a mass
dm of a material by the uncharged particles incident on dm, thus:
dE tr
K
dm
The unit of kerma is joule per kilogram (J/kg) and its special name is gray (Gy).
Kerma approximation
Kerma is sometimes used as an approximation to absorbed dose. The numerical value of the
kerma approaches that of the absorbed dose to the degree that charged-particle equilibrium
exists, that radiative losses are negligible, and that the kinetic energies of the uncharged
particles are large compared to the binding energies of the liberated charged particles.
Lineal energy
The quotient of i by l , where i is the energy imparted to the matter in a given volume bya single energy-deposition event i and l is the mean chord length of that volume, thus

y

i

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l
The unit of lineal energy is joule per meter (J/m)
Linear energy transfer/unrestricted linear energy transfer, L or LET
The quotient of dE by dl, where dE is the mean energy lost by the charged particle due toelectronic interactions in traversing a distance dl thus:dE
Ldl
The unit of linear energy transfer is joule per metre (J/m), often given in keV/µm.
Linear-non-threshold (LNT) model

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A dose-response model which is based on the concept that, in the low dose range, radiation
doses greater than zero will increase the risk of excess cancer and/or heritable disease in a
simple proportionate manner.
Low Earth Orbit (LEO)
Orbit in space near to the Earth where astronauts are protected against parts of particles ofgalactic and solar origin by the Earth magnetic field. The shielding depends on the inclinationof the spacecraft. On the other hand the Earth magnetic field is responsible for the formationof the trapped radiation belts where mainly protons and electrons from galactic and solar
origin are stored.
Magnetosphere
The Earth magnetic dipole field which extends over a distance from Earth up to about
75000 km around the geomagnetic equator. Charged particles in a specific energy range aretrapped in the magnetic field. They move in spirals along the geomagnetic field lines, arereflected back between the magnetic poles acting as mirrors and form radiation belts. Thesebelts were discovered by van Allen.

Mean absorbed dose in an organ or tissue, DT
The mean absorbed dose in a specified organ or tissue T, is given by
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DT 
Ddm ,
mT 
where mT is the mass of the organ or tissue T, and D is the absorbed dose in the mass element
dm. The unit of mean absorbed dose is joule per kilogram (J/kg), and its special name is gray
(Gy).
Nuclear track detectors (NTD)
Detectors where the tracks of passing charged particles can afterwards be made visible bysuitable chemical treatment and microscopically viewed. These passive detectors are either
plastic nuclear etched track detectors (PNTD) where the tracks are made visible by chemical
etching or nuclear emulsions. Etched track detectors are generally insensitive for radiation
with an LET in water below about 10 keV µm-1.
Occupational exposure
The radiation exposure of workers incurred as a result of their work. The Commission limits
its use of ‘occupational exposures’ to radiation exposures incurred at work as a result ofsituations that can reasonably be regarded as being the responsibility of the operating
management.
Operational quantities
Quantities used in practical applications for monitoring and investigating situations
involving external exposure and intakes of radionuclides. They are defined for measurements
and assessment of doses in the body.
Organ absorbed dose
Short phrase for “mean absorbed dose in an organ or tissue”.

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Organ dose equivalent
Short phrase for “dose equivalent in an organ or tissue”.
Organ equivalent dose
Short phrase for “equivalent dose in an organ or tissue”.
Optically stimulated luminescence dosemeters (OSLD)
Detectors where the energy stored by particles in the detector material (glasses) is release asluminescence light by optical laser stimulation. The amount of emitted light is proportional tothe absorbed dose.
Personal dose equivalent, Hp(d)The dose equivalent in soft tissue at an appropriate depth, d, below a specified point on thehuman body. The soft tissue is ICRU 4-element tissue. The unit of personal dose equivalent
is joule per kilogram (J/kg) and its special name is sievert (Sv). The specified point is usually
given by the position where the individual dosemeter is worn. For the assessment of effective
dose, a depth of 10 mm is recommended, and for the assessment of equivalent dose to theskin and the lens of the eye, depths of 0.07 mm and 3 mm, respectively, are recommended.
Protection quantities
Dose quantities related to the human body used for setting exposure limits and in thecontext of optimisation. They have been developed by the Commission for radiologicalprotection to allow quantification of the detriment to people from exposure of the humanbody to ionising radiation from both whole and partial body external irradiation and fromintakes of radionuclides.
Quality factor, Q
A dimensionless factor defined to reflect the relative biological effectiveness of high-LET
radiations compared to low-LET radiation at low exposure levels.
Q is usually given by a function Q(L), where L is the unrestricted linear energy transfer inwater.
The quality factor at a point in tissue, is given by

1
Q( L) DL dL
D L 0where D is the absorbed dose at that point, DL is the distribution of D in unrestricted linear
energy transfer L at the point of interest, and Q(L) is the quality factor as a function of L. The
integration is to be performed over DL, due to all charged particles, excluding their secondary
electrons.
Q

Radiation belt
See “Magnetosphere”.
Radiation weighting factor, wR
A dimensionless factor by which the mean absorbed dose in an organ or tissue, DT, ismultiplied to reflect the relative biological effectiveness of high-LET radiations compared

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with low-LET radiations. The product of wR and DT is the equivalent dose in the organ or
tissue T.

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Reference value
Value of a quantity recommended by the Commission for use in dosimetric applications or
biokinetic models. Reference values are fixed and specified with no uncertainty,
independently of the fact that the basis of these values may include many uncertainties.

Reference male and reference female (reference individual)
An idealised male or female with characteristics defined by the Commission for the purposeof radiological protection, and with the anatomical and physiological characteristics definedin Publication 89 (ICRP, 2002).
Reference person
An idealised person for whom the equivalent doses in organs and tissues are calculated byaveraging the corresponding doses of Reference Male and Reference Female. The equivalentdoses of the Reference person are used for the calculation of the effective dose.
Reference phantom
The computational phantom of the human body (male or female voxel phantom based on
medical imaging data) defined in Publication 110 (ICRP, 2009) with the anatomical andphysiological characteristics defined in Publication 89 (ICRP, 2002).

Relative biological effectiveness (RBE)The ratio of absorbed dose of a low-LET reference radiation to absorbed dose of theradiation considered that gives an identical biological effect. RBE values vary with absorbed
dose, absorbed dose rate and the biological endpoint considered. In radiological protection
the RBE at low and very low doses (RBEM) is especially of interest.
Rigidity, R
The magnetic rigidity of an ion given by its momentum (often given in units of GeV/c)
divided by its charge. Parameter used for characterizing the movement of a high-energy
charged particle in the magnetic field in space.
Rigidity threshold (geomagnetic cut-off rigidity), Rc
For each point inside the Earth´s magnetosphere and each direction from that point there
exist a rigidity threshold below which the cosmic particles are not able to reach this point.
This rigidity is called the geomagnetic cut-off rigidity, Rc.
Solar cosmic radiation (SCR)
Radiation emitted from the Sun. The radiation includes continuously emitted electrons andprotons (solar wind) and also high energy particles (mainly electrons and protons) emitted
during solar particle events (SPE).
Solar cycle
Variation of the solar activity between two extremes with a cycle time of about 11 years.
The solar activity can be described by the number of observed sunspots.

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Solar particle event (SPE)An eruption at the Sun surface that releases a large number of particles (mostly electronsand protons with few helium ions and heavy charged particles) over the course of hours or
days.
Solar wind
Mostly low-energy electrons and protons continuously emitted from the Sun into theheliosphere and producing the interplanetary magnetic field. The intensity of the solar winddepends on solar activity and varies with the solar cycle.
South Atlantic anomaly (SAA)An area where the radiation belt, and hence the trapped protons, comes closer to the Earthsurface due to a displacement of the magnetic dipole axes from the Earth's centre.
Stochastic effect
Effects resulting from damage in a single cell, such as cancer and heritable effects. The
frequency of the event, but not its severity, increases with an increase in the dose. Forprotection purposes it is assumed that there is no threshold dose.
Thermoluminescence detector (TLD)
Small sintered chips or pellets of crystals which show luminescence during heating after
exposure to ionising radiation. By fast controlled heating of the crystal, the stored energy isreleased through light emission. The function between the actual temperature and theintensity of the emitted light (glow curve) shows various peaks, the heights of which areproportional to absorbed dose. These detectors are often used for personal dosimetry.
Tissue reaction
Injury in populations of cells, characterized by a threshold dose and an increase in theseverity of the reaction as the dose is increased further, also termed ‘deterministic effect’. In
some cases, these effects are modifiable by post-irradiation procedures including biologicalresponse modifiers.
Tissue weighting factor, wT
The factor by which the equivalent dose in an organ or tissue T is weighted to represent therelative contribution of that organ or tissue to overall radiation detriment from stochastic
effects. It is defined such that: wT  1 .
T

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Trapped particles
Particles trapped in the Earth's magnetic field as a result of the interaction of galactic
cosmic radiation and solar cosmic radiation with the Earth´s magnetic field and theatmosphere. Mainly protons and electrons are involved (see also “Magnetosphere”).
Voxel phantom
Computational anthropomorphic phantom based on medical tomographic images in which
the anatomy is described by small three-dimensional volume elements (voxels). Collectionsof these voxels are used to specify the organs and tissues of the human body.
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References
ICRP, 2007. The 2007 Recommendations of the International commission on Radiological Protection. ICRP
Publication 103. Ann. ICRP 37(2-4).
ICRP, 2012. Conversion Coefficients for Radiological Protection Quantities for External Radiation Exposures.
ICRP Publication 116, Annals of the ICRP 40 (1).
ICRU, 2011. Fundamental Quantities and Units for Ionising Radiation (Revised). ICRU Report 85a. Journal of
ICRU 11 (1a).

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1.

INTRODUCTION(1)
The radiation field in space is very different from environmental radiation fields on
Earth both with respect to the various types of radiation involved and to their intensities. The
primary radiation field on the Earth surface is composed of low-LET radiations with small
high-LET components including neutrons from cosmic radiation and α-particles emitted fromterrestrial radionuclides. In contrast, the primary radiation field in space includes electrons,
protons, neutrons, α-particles and heavy ions up to very high energies. Additional secondary
radiations (e.g. gamma radiation, electrons, muons, neutrons, pions, and collision andprojectile fragments) are produced by interactions within the materials of a spacecraft and its
equipment and the astronauts themselves.
(2)
The term ”space” generally means the galactic space outside of the aviation altitudes
in the lower atmosphere of the Earth. In manned space flight astronauts may experience
three different exposure conditions. The first situation is in low Earth orbit (LEO) where they
are protected against parts of particles of galactic and solar origin depending on the
inclination of the spacecraft by the Earth magnetic field. On the other hand this magnetic
field is responsible for the formation of the trapped radiation belts. In addition, throughinteraction of the solar and galactic particles with the nuclei of the Earth´s atmosphere albedo
radiation is created. Secondly, leaving the Earth magnetic field to outer space ininterplanetary missions, the radiation exposure due only to particles of solar and galactic
origin, which are directly impinge on the spacecraft. In planetary missions, about one
hemisphere is shielded by the mass of the planet. If there is no atmosphere, the primaryradiation interacts with the nuclei of the soil which leads to the production of secondary
particles with a high contribution of high-LET components. If a thin atmosphere is present, as
in case of Mars, both interactions in the atmosphere and in the soil contribute to secondary
radiation.
(3)
Astronauts are living and working in low Earth orbits for extended periods of time
and will be involved in outer space missions. They are living under extraordinarily different
environmental conditions than ever encountered on Earth. For missions outside themagnetosphere, ionising radiation is recognized as the key factor through its impact on crew
health and performance. Obviously the radiation environment is quite different from that on
Earth and human exposure in space is much higher than on Earth and cannot be avoided byradiation shielding. The reasons for that are the extreme high energies of particles in spaceradiation fields and their high penetration depth in matter combined with the release of
secondary radiations (e.g. neutrons and photons) in interactions of the primary radiation withthat material. The exposure of astronauts in space is a special case of environmental
exposure. In long term missions, the exposure of astronauts will be higher than the annual
limits recommended for exposure of workers on Earth. In ICRP 103 it is stated that “inexceptional cases of cosmic radiation exposures, such as exposure in space travel, where
doses may be signiﬁcant and some type of control warranted, should be dealt withseparately”. Therefore, although astronauts are exposed to ionizing radiation during theiroccupational activities they are usually not classified as being occupationally exposed in thesense of the ICRP system for radiation protection. Their situation during space missions issimilar to special planned exposure situations in emergency exposure situations, in which socalled rescuers may be exposed to radiation levels during their intervention exceeding dose
limits for occupationally exposed persons. Thus, for a specific mission planned, reference
values for risks or doses may be selected at appropriate levels and no dose limits may be
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applied for the given mission.
(4)
During the last two decades there was a marked development in the activities inspace including an increase of the number of astronauts participating in space missions.
Nevertheless, even today, the number of astronauts is small as compared to the large numberof occupationally exposed persons on Earth and in civil aviation. However, considering theextraordinary exposure situation of this group, radiological protection concepts need to bewell defined and realistically implemented with respect to the specific situation found in thespace environment and during long-term space missions.
(5)
The basis for any measure in radiological protection should always be theknowledge of the radiation fields involved. Therefore, measurements of the environmental
radiation and the assessment of the exposure of astronauts are very important tasks. Since thediscovery of cosmic radiation at the start of the last century by V.F. Hess in 1912 (see e. g.
Compton, 1936) the study of cosmic radiation and its various components has already been
performed for a long time and has become even more important during the last fifty years
when activities in space are strongly increasing and frequently include the presence ofastronauts. Obviously the basic information regarding cosmic radiations and their various
components can only be obtained through measurements and this has been performed formany years. The specific environmental situation in and around a spacecraft can be estimatedeither by various measurements at different positions in the specific spacecraft or also byradiation transport calculations when the spacecraft design is sufficiently modelled and thespecific composition of the external radiation field including its variation in time is wellconsidered within the simulation code applied. Some parts of this report, therefore, deal withthe various components of the radiation field in space (Chapter 2) and with the computercodes and calculational approaches used to simulate both radiation shielding possibilities forthe various radiation fields incident upon the spacecraft and the resulting tissue absorbed
doses imparted to the astronauts within the spacecraft (Chapters 5 and 6).
(6)
The specific radiation field in space with its important contribution of heavy ionsdoes not allow simple application of the complete system of dosimetric quantities defined foruse in radiological protection on Earth. The radiation weighting factor of 20 defined for all
heavy ions of all energies is not appropriate, nor is the concept of the operational dosequantities for external exposure situations applicable to the space situation because very highenergy particles are involved. The concept of operational quantities has been introduced by
the ICRU and ICRP mainly looking at electron, photon and neutron radiations of energies up
to few tens of MeV and has not considered radiation fields in space which include manyother particle types with even higher energies. This topic will be discussed in more detail in
Chapter 3.
(7)
On Earth, radiological protection of workers and the primary dose limits defined are
aimed at limiting the probability of the occurrence of stochastic effects, e.g. risk of cancer orhereditary effects, to a level acceptable when compared to other health risks during human
life, while at the same time avoiding detriments in humans by deterministic effects (tissue
reactions). For practical reasons the primary limits are defined in terms of doses (effective
dose and equivalent dose to the skin, hands, feet and lens of the eye where specific limits
have been defined for avoiding deterministic effects) which can be assessed with sufficientprecision for applications in radiological protection, and not in terms of radiation risks thevalue of which depends on many individual factors (e.g. age, sex, individual genetic
properties). Especially at low levels of exposure, the knowledge regarding these risks is very
limited and combined with high uncertainties. The value of the quantity effective dose iscalculated by averaging organ equivalent doses over both sexes and using mean values of18

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weighting factors obtained from epidemiological data, hence from large groups of exposed
and unexposed persons. Effective dose should, therefore, not be used for the assessment of
individual risks. In addition to “limitation” of doses and risks the principle of ALARA (AsLow As Reasonably Achievable) is generally applied in radiological protection which meansthat even below exposure limits “optimisation” of radiation protection always needs to beconsidered and may require further measures.
(8)
The situation in space is quite different. An exposure of astronauts by environmental
radiation cannot be avoided in space. Prevention by shielding cannot be completely achieved.
Nevertheless, optimisation of radiation protection is an important task, especially because inlong-term missions doses to astronauts may exceed 100 mSv. The occurrence of deterministic
effects can also not generally be excluded. In addition, the knowledge of radiobiologicaleffects of cosmic radiation in particular heavy ions is very limited. The number of persons
involved is small and hence individual risk assessment is of much higher interest. As aconsequence, values of mean absorbed doses in organs and tissues of the human body play animportant role, since the weighting factors used in the definition of effective dose orequivalent dose in an organ or tissue are not appropriate in the radiation field in space. In
addition, for many years, the use of organ dose equivalent has been preferred by many space
agencies instead of the quantity equivalent dose in an organ (see Chapter 3).
(9)Both radiation monitoring in the spacecraft environment and assessment of doses in
the human body of astronauts are important parts of the radiological protection measures inspace missions. Due to the complex radiation field and the special requirements for use inspace flight radiation monitoring needs specific measurement devices and procedures.
Usually, more than a single dosemeter type is needed for this task and often additional
calculations are necessary to interpret device response (see Chapters 4 and 6).
(10) Calculation of conversion coefficients which relate values of particle fluence or dose
external to the human body to values of absorbed dose and mean quality factors in organs andtissues within the body is an important task and is often used for the assessment of doses inthe body from external measurements. While reference data on conversion coefficients
related to the reference voxel phantoms defined in ICRP Publication 110 have already been
published by the Commission in Publication 116 (ICRP, 2011), data for heavy ions havebecome available only recently (Sato et al., 2010). In this report data are presented for
isotropic exposure of both male and female voxel phantoms. Omni-directional exposure(ISO) is the most realistic exposure situation in space. While shielding effects may result in amore non-isotropic exposure, the movement of the astronauts within the spacecraft balances
this situation. Hence, data are presented for ISO exposure only (see Chapter 6 and theAnnex). The use of conversion coefficients is, however, not the only method in assessingorgan doses in the body. Based on knowledge of the radiation field outside a spacecraft,
calculation of organ doses can be performed including the full radiation transport through thewalls and the equipment of a spacecraft (see Chapter 6).
(11) While on Earth biological dosimetry is mainly restricted to applications in accidental
exposure situations due to the usually low doses of occupationally exposed workers and the
difficulty in measuring doses below about 50 mSv by this method with acceptable
uncertainty, the situation in space is quite different. Mission doses may be above that“threshold” and biological dosimetry (e.g. study of biological effects on lymphocytes in thehuman body) allows a very individual assessment, if in advance the individual sensitivity isdetermined and hence an individual calibration is performed. Methods and measurements are
discussed in both Chapters 4 and 6 of the report.

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2. RADIATION ENVIRONMENT IN SPACE(12) The radiation environment in space is a complex mixture of particles of solar andgalactic origin with a broad range of energies. For radiological protection, the relevant
radiation fields are the galactic cosmic radiation (GCR), particles ejected from the Sun duringsolar energetic particle (SPE) events, and secondary radiation produced through interaction
with the planet’s atmospheric nuclei. Solar wind particles, even when enhanced due to higher
solar activity, do not significantly contribute to the radiation exposure to man due to theirrelative low energy and hence their absorption in already very thin shielding materials.
Nevertheless, the solar wind modulates the fluence rate of galactic cosmic radiation in theenergy range below about 1 GeV/u. During phases of higher solar activity, the cosmic
radiation fluence rate is decreased by a factor of three to four compared with phases during
minimum solar activity.
(13) Presently, there is no measurable contribution to the radiation exposure by primaryelectromagnetic ionising radiation such as from solar Roentgen flares like that which
occurred on November 4th 2003 UTC 19:29 or from conspicuous extreme gamma radiation
bursts such as that which occurred on December 27th 2004 UTC 21:30:26.55; hence, they areomitted, although on geological time scale, their impact on the biosphere might have beensignificant. Secondary electromagnetic radiation of course contributes as bremsstrahlung
emitted from charged particles upon penetration though matter and as gamma radiation fromthe decay of neutral pions π0 created in the Earth´s atmosphere.
(14) From the point of view of radiological protection, the focus is on the particulatecomponents of space radiation of ions and electrons only. Electrons might become relevant
during extravehicular activities (EVAs) or if manned activities in the outer radiation belts
become an issue which, however, will not be the case for the foreseeable future.
(15) Through the Earth´s magnetic field and an atmospheric shield with a thickness ofabout 1000 g cm-2, the exposure to cosmic radiation on the Earth surface is reduced to anegligible level. Leaving Earth, astronauts are shielded by the structure of the spacecraft andits interior by an average of about 20 g cm-2, a shielding close to that of the Martian
atmosphere, but when in low Earth orbit, they are still protected by the Earth´s magnetic field
which limits even the exposure to solar energetic particles to a level far below the cause ofearly radiation effects in man.
(16) In the absence of sporadic solar particle events, the radiation exposure in near Earthorbits inside spacecraft is determined by the galactic cosmic radiation (protons and heavierions) and by the protons inside the South Atlantic Anomaly (SAA), an area where theradiation belt comes closer to the Earth surface due to a displacement of the magnetic dipole
axes from the Earth's centre. In addition, there is an albedo source of neutrons produced asinteraction products of the primary galactic particles with the nuclei of the Earth atmosphere.
Outside the spacecraft, the exposure of astronauts is dominated by the electrons of the hornsof the radiation belt located at about 60° latitude in Polar regions.
(17) All these radiations from different sources and their interactions by various
mechanisms determine the actual field of ionising radiation at any given time and location
within the heliosphere. Its complexity is unrivalled by anything we know from terrestrial
experience. The radiation field inside a spacecraft is even more complex through theinteraction of the high energy particles with the spacecraft shielding material and the bodytissues of the astronauts.

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(18) In deep space missions the Earth´s radiation belts will be crossed in a couple ofminutes and therefore its contribution to their radiation exposure is quite small. However, thesubsequent protection by the Earth´s magnetic field is then lost, leaving only mission
planning and shielding measures as a means of exposure reduction. The following sections
describe the radiation field in space and the interaction of the charged particles with themagnetic field and shielding materials. Some numbers are given on the radiation exposure in
low Earth orbits and in interplanetary missions.
2.1

Primary radiation fields(19) Three major primary sources of radiation can be specified in space.
 The solar system with the Sun at its centre is embedded in a complex mixture ofionising radiation, galactic cosmic radiation (GCR), which continuously enters theheliosphere from all directions. Inside the heliosphere, the GCR fluence rate andparticle energy distributions are modulated by the interplanetary magnetic field
produced by the charged particles continuously emitted by the Sun, the so-called solarwind.
 In addition to the solar wind, the Sun occasionally emits unusually large pulses ofenergetic particles – mostly protons and electrons with a small and variable
contribution from helium and heavy ions - ejected in to space by these solar eruptions.
The most significant of these solar-particle events (SPEs) are produced by the
expulsion of large amounts of material in coronal-mass ejections (CMEs).
 Celestial bodies equipped with a magnetic moment like the Earth are surrounded bytoroidal belts of particulate radiation which are constantly replenished by solar particles
and secondary particles caused by the interaction of solar and galactic particles with theatmosphere. Such radiation belts constitute an important third primary exposure source.
(20) Figure 2.1 illustrates these three sources of ionising radiation in space, theirrespective spatial scales and the dominant role the Sun plays in modifying its composition.
The highest energies measured for GCR particles (Fig. 2.1) are too large to be compatible
with their postulated acceleration and containment by intra-galactic magnetic fields thereby
giving rise to speculations about extra-galactic sources for this part and hence extending the
spatial scales even further. The corresponding intensities, however, are too low to contribute
substantially to radiation exposures.

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Integral fluence rate / cm-2 s-1

1015

Solar wind protons
Auroral electrons

1015

1015

Trapped protons(outer zone)

Trapped protons(inner zone)

Solar storm protons

1015

1015
10-4

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Trapped electrons

Solar flare protons

Galactic cosmic radiation

10-2

100

102

104

Particle energy / MeV
Fig. 2.1. Synoptic view of integral particle fluence rate of space radiation versus upper boundary ofparticle energy (Wilson, 1978).

(21) In addition to their variation with location in space, the intensity and particulatecomposition in these fields are subject to temporal variations. As far as space radiation isconcerned, two temporal scales of space weather events are relevant. Similar to the annual
alternation between summer and winter of ordinary weather on Earth, we have to deal with anearly regular change of solar activity between phases of maximal (‘summer’) and minimal(‘winter’) solar activity. The solar ‘year’ in this case is the Schwabe cycle, a period of about
11 years the duration of which however (presently) varies due to so far unknown mechanisms
between 9 and 13.6 years. One measure of this activity for which a continuous observational
record exists since 1755 is the Zürich sunspot number (Hathaway et al., 2002). Apparently,
the maximum of solar activity is inversely associated with the length of the cycle. In addition
to the field variation during the regular solar cycle, episodes of extreme solar activity
characterised by explosive releases of magnetic energy (Chen, 2001) which eject giant
masses of charged particles from the Sun´s corona into the interplanetary magnetic field.
After further acceleration in this field, particle energies up to several GeV can be attained.
The impact of these solar particle events (SPE) on the radiation field in space can last fordays to some weeks.
(22) Further observed solar periodicities like the magnetic Hale cycle of 22 years, theGleisberg cycle of about 88 years or the De Vries- or Suess cycle of about 210 years have notyet been identified to substantially modulate the radiation field, although their impact on thebiosphere probably is important as a recent study on glacial climate cycles discloses (Braunet al., 2005).
2.2

Galactic cosmic radiation(23) Galactic cosmic radiation originates outside the solar system and impinges
isotropically on Earth. There is no conclusive proof of the mechanisms accelerating thecharged particles and of the astrophysical sites where matter becomes cosmic particle
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radiation. There is no information about the directional position of their sources since theseparticles are scrambled by irregular interstellar magnetic fields on their way towards the
Earth. Because of their high energies - up to 1020 eV - they most probably originate fromsupernova explosions, neutron stars, pulsars or other sources where high-energy phenomena
are involved. Detected radiation consists of 98% baryons and 2% electrons. The baryoniccomponent is composed of about 85% protons (hydrogen nuclei), with the remainder beingalpha particles (about 14%) and heavier nuclei (about 1%). Figure 2.2 shows the abundancesof these elements up to tin relative to silicon. The ions heavier than alpha particles are termed
HZE-particles (high charge, with charge numbers Z>2 and high energy). Although iron ionsare one-tenth as abundant as carbon or oxygen, their contribution to absorbed dose in tissue issubstantial, since this dose is proportional to the square of the particle charge. This isindicated in Fig. 2.2 (Cucinotta et al, 2001).
(24) In addition to the galactic cosmic radiation, a so-called anomalous component isobserved. It consists of originally neutral particles coming from the interstellar gas whichbecome singly ionised by solar radiation after entering the heliosphere. These particles arethen accelerated in collision regions between fast and slow moving streams of the solar wind.
They are able to penetrate deeper into the magnetic field than fully ionised cosmic particles.
Their energies are around 20 MeV/u and consequently they can only contribute to radiation
effects behind thin shielding. However, it has to be considered that they lose all theirelectrons after penetration of a very small amount of shielding material and thus also deposit
energy proportional to the square of their charge number Z.

Relative contribution%──── Fluence…… ….... Absorbed dose
– –■ – Dose equivalent

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Charge number
Fig. 2.2. Elemental composition of galactic charged particles and their relative contribution toabsorbed dose and dose equivalent in tissue (Cucinotta et al, 2001).

(25) In this report energies of GCR nuclei are always presented as kinetic energy peratomic mass unit (amu or u), E. This has the advantage that all nuclei having the same valueof energy per amu move with nearly the same velocity regardless their mass. Using thisenergy scale the energy distributions of the different cosmic ray nuclei are very similar.

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913

Fluence rate distributions in energy for hydrogen, helium, carbon and oxygen, and iron are
shown in Fig. 2.3. At energies E above some GeV/u the fluence rate is well represented by apower law N(E)~ E--γ with γ around 2.5. Towards lower energies the distributions get flatterand show a maximum at about some hundred MeV/u.

Spectral fluence rate / (m2 sr1 s1 MeV/u) -1

101
Minimum
Maximum

100
10-1
10-2
10-3
10-4
10-5

10-6
10-7
10-8

101

914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940

HydrogenHeliumOxygen
Iron

102

103

104

Particle energy/ MeV u-1

105

106

Fig. 2.3. Energy distribution of fluence rate versus particle energy for 4 GCR particles and theirmodification by solar activity (for solar minimum (1977) and solar maximum (1959)) at 1 AU as
relevant for radiological protection (Badhwar, 1997).

(26) Fluence rates of cosmic radiation are not constant; they vary between two extremes
which correspond in time with the maximum and minimum solar activity. Solar activity andcosmic radiation fluence rates are inversely correlated. The slope of the energy distribution in
Fig. 2.3 for energies below some GeV/u is affected by this modulation of the cosmic
radiation fluence rate (Badhwar, 1997). It is caused by the solar magnetic field, which is
coupled to the solar wind. The solar wind is a continuous stream of highly-ionised plasma
emerging from the Sun. Its intensity depends on solar activity which can be described by the
number of observed sunspots. During the minimum of the 11-year solar cycle the solar wind
has a minimum strength and its effect on the energy distribution is smaller than at maximum
solar activity. Cosmic particles incident on the solar system interact with the solar magnetic
field and thus lose energy. This leads to flattened energy spectra at lower energies. With
increasing solar activity, the maximum of the fluence rate is shifted to higher particle
energies. At 100 MeV/u, the particle fluence rates differ by a factor of about 10 between
maximum and minimum solar activity conditions, whereas at about 4 GeV/u only a variationof about 20% is observed.
(27) Monitoring of solar modulation is possible on Earth based on the fluence rate ofsecondary neutrons produced in the Earth's atmosphere by interactions of galactic cosmic
radiation. This fluence rate has been measured over longer periods by different ground based
stations using neutron monitors. Figure 2.4 shows an example of data taken over several
years with the neutron monitor at Kiel University (NMDB, 2011). It can be seen that detailsof the modulation seem to be unpredictable statistical fluctuations. However, maxima andminima clearly appear inversely correlated to the 11-year solar cycle with a roughly
25

DRAFT REPORT FOR CONSULTATION
Fig. 2.4

sinusoidal form around an average particle fluence rate. However, the magnitude of theextremes again undergoes fluctuations. Predictions for future satellite missions are limited inaccuracy within a factor of two or even more based on such unpredictable fluctuations.
Relative GCR fluence rate in %

941
942
943
944

945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975

+10
+5
0
-5
-10

-15
-20
-25

-30
-35
1960

1970

1980

1990

2000

2010

Year
Fig. 2.4. Relative fluence rate variation of cosmic radiation (GCR) with time in the solar cycle ofthe heliocentric potential measured by the neutron monitor in Kiel (NMDB, 2011).

2.3

Solar cosmic radiation(28) Besides electromagnetic radiation, the Sun continuously emits particle radiation,
mainly consisting of protons and electrons, the solar wind. The intensities of these low
energy particles vary by 2 orders of magnitude between about some 1010 and 1012 particles
cm-2 s-1 sr-1. In terms of velocity, this particle stream is characterised by velocities between
about 300 km s-1 and 800 km s-1 and more. The particle energies, however, are so low (forprotons between 100 eV and 3.5 keV), that the particles will be stopped within the first few
microns of unshielded skin. They are, therefore, not of concern for radiation effects in man.
(29) Nevertheless, the temporal variation of the solar wind is a major driver which
determines radiation exposure from GCR in space, at least within the inner heliosphere. The
heliosphere itself can be defined as that domain of the interstellar space which the solar wind
can fill out. The magnetic field based on the solar wind provides a similar shielding as thegeomagnetic field does. The shielding strength can be simulated in terms of a pseudoelectrostatic heliocentric potential against which the charged particles have to work whenentering the heliosphere from the local interstellar medium. This potential modifies the GCR
energy spectra to the same degree as the interplanetary magnetic field does.
(30) Occasionally, the surface of the Sun releases large amounts of energy in sudden
local outbursts of gamma radiation, hard and soft x-rays and radio waves in a wide frequency
band. In these solar particle events (SPEs), large currents and moving magnetic fields in thesolar corona accelerate solar matter. Coronal particles with energies up to several GeV escape
into the interplanetary space. They spiral around the interplanetary magnetic field lines.
Within the ecliptic plane, field lines expand from the Sun into the interplanetary medium likethe stream of water from a rotating garden hose. They connect the Earth with a certain spot
on the western part of the Sun. The number and energy distribution of particles observed insolar particle events at Earth is different from GCR and depends on this connection. SPEs

26

DRAFT REPORT FOR CONSULTATION
show an enormous variability in particle fluence rates and energy distribution and have thepotential to expose space crew to high life-threatening doses(31) An SPE well-connected with high particle fluence rates observed at Earth is an
infrequent event which is most likely to be observed during the period of increasing anddecreasing maximum solar activity. Therefore, major SPEs are observed at Earth as random
events with a low frequency, typically one per month. They last for several hours or days.
Events with significant fluence rates of protons with higher energies can be observed as"ground-level events" (GLE) by neutron monitors. Figure 2.5 shows the number of GLEs
observed over the last solar cycles. Long gaps with no events can be seen during solar
minimum activity. Between the last GLE in cycle 21 and the first one in cycle 22 there was a
65 month quiet period which was followed by a sequence of 11 GLEs within one year withapproaching maximum of the present solar cycle.

 p >100 MeV

 p >80 MeV

 p >30 MeV in cm-2

976
977
978
979
980
981
982
983
984
985
986
987
988

989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004

Cycle 19

20

21

22

23

Date
Fig. 2.5. Occurrence of major solar particle events in solar cycles No. 19 to 23 and the integral
particle fluence, p, for protons with energies >30MeV, >60MeV, and >100MeV (Kim et al., 2011).

(32) Since high energetic particles arrive first and are followed by particles of lower
energies, the energy distribution of SPE particles observed at Earth depends on time after
onset of the event. Above energies of about 10MeV, SPE particle spectra following
approximately the power law I(E)=I0 E-. After the onset of the event, the exponent γ
decreases with time. This means that the contribution by high-energy particles decreases withtime during the event. The constant I0, describing the absolute number of particles, shows agreat deal of structure during the event caused by field irregularities and shock structures in
the interplanetary medium.
(33) Such events can induce adverse skin reactions in astronauts if they get caught
outside shielding since above about 10 MeV protons can penetrate space suits and reach theskin or the lens of the eye. Depending on the particle intensities they may induce erythema or
trigger late radiation cataracts within the lens of the eye. While the latter take several years to27

DRAFT REPORT FOR CONSULTATION
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018

develop and hence pose no threat to a safe mission completion, severe erythema may wellinduce performance decrements which could compromise mission success.
(34) Since 1955, five SPEs with intensities and energies large enough to jeopardise crew
health behind normal or even enhanced spacecraft shielding have so far been observed. For
these strong events integral fluence distributions (total number of particles per unit area
above an energy E) have been measured by satellite instruments (see Fig. 2.6). For a sixth
event - that of February 23rd 1956 - the fluence distribution has been inferred from ananalysis of the count rates of terrestrial neutron monitors which recorded the induced
secondary neutrons. Such enhancements of neutron count rates are monitored in a worldwide
net of neutron monitor stations a selected subset of which forms the so called Spaceship
Earth. Ground level enhancement (GLE) events indicate that associated SPE protons withenergies above about 450 MeV were sufficiently numerous to raise the neutron fluence rate at
sea level by at least 5%.
1111
10
1.00E+11
10

Integral proton fluence 2(>Ep) / cm-2

1010
1.00E+10
10
10

1099
1.00E+09
10 >E, protons/cm

1.00E+08
1088
10February 1956

1.00E+07
10
1077

November 1960
September 1989

1066
1.00E+06
10

October 1989

August 1972

1.00E+05
1055
10February 1956
November 1960
August 1972
September 1989
October 1989

1.00E+04101044

1.00E+03
101033
1.00E+02
10
1022

10
10
10

1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034

102
100
100

E, MeV

103
1000
1000

5000

Proton energy / MeV

Fig.2.6.
Integral fluence spectra of protons from historical ‘worst-case’ solar particle events (Kim etal., 2010a).

(35) A comprehensive list of GLE´s observed since February 23 rd 1956 (GLE No. 5) andJuly 14th 2000 (GLE No. 59) together with all neutron monitor stations where these eventswere observed is provided by the Australian Antarctica Data Centre(http://data.aad.gov.au/aadc/gle/events.cfm). Among all these GLEs, the enhancement by
GLE No. 5 in Leeds (lat.: 53.83 N, long.: 358.42 E, alt.: 100 m, Pc=2.20 GV) is about 4600%
higher than the pre-event count rate, whereas for other SPEs the enhancement very rarely
exceeds a 100% increase.
(36) A small fluence rate of solar particles with low energies also reaches the Earth from
SPEs at other positions of the Sun which are not fully directed to the Earth. These fluence
rates add up to a solar component which dominates over the galactic component at energies
below 30 MeV/u. Depending on the conditions of the interplanetary medium, thiscomponent undergoes fluctuations which are highly variable and unpredictable. During
28

DRAFT REPORT FOR CONSULTATION
1035
1036
1037
1038
1039
1040
1041
1042
1043

periods of maximum solar activity, when the fluence rate of galactic cosmic radiation isdepressed and SPEs are more frequent, the contribution of the solar component is moresignificant.
(37) For long-term mission planning, in addition to the magnitude that a worst case event
can attain, the frequency of occurrence of events as well as the proton energy spectrum
becomes important too. Fig. 2.7 gives a probability that a particle event with protons ofenergies above 30 MeV occur, based on the random nature of SPE occurrence and event sizeand based on the records taken for fluence measurements of the last five solar cycles.
1.0 1

19
 CycleCycle
19
Cycle 20
 Cycle
Cycle
20
21
22
 CycleCycle
21
Cycle 23
 Cycle 22
Impulsive Nitrate Events
 Nitrate
Cycle
Events 23
with Correction
Space
era
— Space era

0.90.90.80.80.60.6
Probability

Probability

0.70.70.50.50.40.40.30.30.20.20.10.1
0.0 0
104 4
10

1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064

1055
10

1066
10

1077
10

108 8
10

1099
10

10
1010
10

Eventenergy
Size ( 30), p >30
cm-2 MeV per event / cm-2
Fluence of protons with

Fig. 2.7. Probability of an SPE event with protons exceeding the energy of 30 MeV versus proton
fluence per event for different cycles and for the complete space era (Kim et al., 2011).

2.4

Trapped radiation(38) The radiation field around the Earth comprises the third radiation source. The
particles trapped in the radiation belts discovered by van Allen are a result of the interactionof GCR and SCR with the Earth's magnetic field and the atmosphere. The radiation belts
consist of electrons and protons, and some heavier ions. Electrons reach energies of up to 7
MeV and protons up to 700 MeV. The energy of heavy ions is less than 50 MeV/u, andbecause of their limited penetration capacity, they are of no consequence for satellite
electronics or radiological protection of humans. Charged particles with these energies
moving into a dipole field can never enter into inner areas of this field. However, if they are
put into this field for any reason, they are restricted to certain positions and cannot escape.
They move in spirals along the geomagnetic field lines and are reflected back between themagnetic poles, acting as mirror points. Different processes contribute to fill in particles into
the radiation belt and two main zones of captured particles are observed. The inner belt ismainly formed by decaying neutrons, coming from the atmosphere in which they are
produced in cosmic particle interactions, and producing protons and electrons. The outer belt

29

DRAFT REPORT FOR CONSULTATION
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107

consists mainly of trapped solar particles, and is populated largely by electrons. During
disturbances of the magnetosphere by magnetic storms related to solar flares, where thegeomagnetic cut-off is usually depressed, particles of lower energies can penetrate fromoutside towards the inner regions and fill them. The radiation belts extend over a distancefrom Earth from about 200 km to about 75000 km around the geomagnetic equator. Energy
loss by cyclotron radiation and by penetration into the upper atmosphere near thegeomagnetic mirror points constitutes the major loss mechanisms for the trapped particle
population.
(39) Extensive measurements during the recent decade with more advanced anddedicated instrumentation on several satellites in well-coordinated orbits yielded the main
quantitative database which then became integrated in the AP-8 TRAPPED PROTON
MODEL (Sawyer et al., 1976) and which provides energy spectra of average proton fluence
rates during quiet magnetospheric conditions. A major application which these models havebeen designed for is the assessment of the radiation exposure from trapped radiation during
manned low Earth orbit (LEO) missions such as presently on the International Space Station(ISS). The AE-8 TRAPPED ELECTRON MODEL (Vette, 1991) serves the same purpose ofprediction radiation doses yet mainly for the radiation environment in geostationary orbits
where energetic electrons constitute the dominant source of ionising radiation.
(40) An improved AE-9/AP-9 Model is being developed as part of the Proton
Spectrometer Belt Research (PSBR) Program and is planned to be released in near future by aconsortium of institutions, such as the National Reconnaissance Office (NRO), Aerospace
Cooperation, the Air Force Research Laboratory (AFRL), Los Alamos National Laboratory(NAL) and the Naval Research Laboratory NRL).
(41)
There is a strong east-west effect in trapped proton fluence rates. At the bottom of
their path around the magnetic field lines, protons are travelling eastwards, whereas those on
the top of their path are travelling westwards. The westwards travelling particles haveemerged from a region of the atmosphere at lower altitude. Therefore, they encounter adenser atmosphere and are more efficiently removed by interactions with the nuclei of theatmosphere (Lenchek and Singer, 1962).
(42) Figure 2.8 displays the spatial distribution of electron fluence rate for electronenergies above 0.5 MeV (right) and of proton fluence rate for proton energies above 34 MeV(left) at which energy the latter are able to penetrate about 1.4 g cm-2 Al, the shielding
provided by lighter space craft. Proton fluence rates in the inner belt are intense and protons
reach sufficient energies to penetrate the shielding provided by walls and equipment of space
craft so that primarily their energy distribution as shown in Fig. 2.9 have to be known inorder to assess radiation exposures of astronauts. The data in Fig. 2.9 are the results ofmeasurements of the energy distribution of trapped proton fluence rate in the early 1960s(Filius, 1965; Freden et al., 1964). As a natural coordinate system to specify the satellite
position within the geomagnetic field, the (B, L) coordinates are used. Here, B denotes themagnetic field strength at a given point and L the altitude in units of Earth radii at which themagnetic field line through this point intersects the plane through geomagnetic equator.

30

DRAFT REPORT FOR CONSULTATION

Geomagnetic axis

Earth

AltitudeElectron fluence rate (cm -2 s-1)
Ee > 0.5 MeV

Proton fluence rate (cm -2 s-1)
Ep > 4 MeV

1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118

Fig. 2.8.
Fluence rates in inner and outer terrestrial radiation belts for trapped protons andelectrons in cm-2 s-1 (Allkofer, 1975).

(43) Figure 2.10 shows the fluence rate energy distributions of trapped electrons andprotons averaged over the orbit of the Hubble Space Telescope. Electron fluence rates duringsolar maximum are greater than during solar minimum, pointing to the Sun as the dominantprimary source which feeds the trapped electron population. In contrast, the trapped proton
fluence rates reflect the (Forbush) modulation of the GCR intensity by the solar wind which
results in higher intensities during solar minimum conditions.

31

DRAFT REPORT FOR CONSULTATION
1119
106

∆

Proton fluence rate / cm-2 s-1

January 1963
August 1964
 June 1966

105
(A)
L = 1.6
B = 0.0797(B)
L = 1.4
B = 0.209

103(F)
L = 1.8
B = 0.2295

102

10

20

40 60 80 100 200

1020

L = 2.0
B = 0.0849

40 60 80 100

200

Proton energy / MeV

1011

1010
109

108
107

106
105

104

Electron energy / MeV

Mean spectral fluence rate / (cm2 MeV d)-1

2.9
Fig. 2.9. Fig.
Fluencerate spectra of inner belt protons measured at various locations within the belts as
expressed in the B,L-coordinate system (Filius, 1965; Freden et al., 1964).

Mean spectral fluence rate / (cm2 MeV d)-1

1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136

(E)

(C)
L = 2.0
B = 0.226

101

1120
1121
1122

(D)
L = 1.8
B = 0.073

104

107

106

105

104

103
10-1

102

103

104

105

Proton energy / MeV

Fig. 2.10. Left: Mean energy distribution of fluence rate of trapped electrons at solar minimum andmaximum conditions calculated with the AE-8 model for the position of the Hubble space telescope(Jones, 2000).
Right: Mean energy distribution of fluence rate of trapped protons at solar minimum and maximum
conditions calculated with the AP-8 model for the position of the Hubble space telescope (Jones,
2000).

(44) The fluence rates and energy distributions shown pertain to quiet magnetic
conditions of the terrestrial and interplanetary magnetic field during the minimum andmaximum of solar activity. In addition to the regular solar cycle variation, both magnetic
storms and intensive fluence rates from energetic solar particle events (SPE) significantly
shift positions and energies of trapped particle populations so that even additional thoughtransient radiation belts can be created.

Fig. 2.10

32

DRAFT REPORT FOR CONSULTATION
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171

(45) The trapped radiation is modulated by the solar cycle: with increasing solar activity,
proton intensity decreases, while electron intensity increases. Diurnal variations by a factor of
between 6 and 16 are observed in the outer electron belt, and short term variations due tomagnetic storms may raise the average fluence rate by two or three orders of magnitude. The
centre of the inner belt is quite stable, especially with respect to protons. However, at thelower edge of the belt, electron and proton intensities may vary by up to a factor of 5. For the
majority of space missions in low Earth orbit (LEO), protons are an important part of theradiation exposure inside spacecrafts. Because of their higher energies and correspondingly
longer range, their total dose surpasses that of electrons at shielding thickness above about
0.3g/cm2 aluminum. At lower shielding, e.g. in case of extravehicular activities (EVA), theabsorbed dose to the skin is dominated by the electron contribution and may reach up to
10mGy per day.
(46) Of special importance for low Earth orbits is the so called 'South Atlantic Anomaly'(SAA), at the moment a region over the coast of Brazil, where the radiation belt extends
down to altitudes of 200 km. This behaviour is due to an 11° inclination of the Earth's
geomagnetic dipole axis from its axis of rotation towards northern America and a 500 km
displacement of the dipole centre towards the western Pacific, with corresponding
significantly reduced field strength values. Radiation received in LEO at low inclinations
includes GCR and radiation due to passages through the SAA. At an orbit with 28.5°
inclination, six orbital rotations per day pass through the anomaly, while nine per day do not.
Although traversing the anomaly takes less than about 15 min and occupies less than 10% of
the time in orbit, this region accounts for a significant fraction of total exposure.
(47) In addition to the trapped charged particles in radiation belts, the GCRs are producing
secondary neutrons by nuclear reactions in the upper atmosphere of the Earth. Neutrons areproduced in practically two energy regions by two processes. Neutrons in the region between 1
and 10 MeV are mostly evaporation products of highly excited nuclei with a fairly isotropic
angular distribution. High-energy neutrons originate as knock-on neutrons mainly in peripheral
collisions or in charge exchange reactions of high-energy protons. Their energy distribution
peaks at about 100 MeV. They leak into the exosphere and contribute also to the exposure inspacecraft. Measured neutron spectra in the Earth atmosphere are shown in Fig. 2.11. Their
contribution to the radiation field in LEO is, however, relatively low. A similar neutron field asmeasured in the atmosphere is of course produced by interactions of the GCR with thespacecraft material and the astronaut’s body. This contribution to the exposure of astronauts issubstantial (Bartlett et al., 2006).

33

DRAFT REPORT FOR CONSULTATION
1.4
20 km ( 56 g/cm2 air)
16 km ( 100 g/cm2 air)
12 km ( 200 g/cm2 air) x 2.8
16 km (1010 g/cm2 air) x 700

E d /dE / (cm-2 s-1)

1.2



1.0
0.8
0.6
0.4
0.2
0.0
10-9

1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204

10-7

10-5

10-3

10-1

101

103

105

Neutron energy / MeV
Fig. 2.11

Fig. 2.11. Neutron spectra from cosmic radiation on ground and in different atmospheric depths at
air flight altitudes measured with Bonner spheres during the AIR ER 2 flights and on the ground at
sea level (Goldhagen et al., 2004).

2.5Interaction with magnetic fields(48) To reach spacecraft in low Earth orbits (LEO) a charged particle has to penetrate theEarth's magnetic field. Penetrability is a property related to the ions magnetic rigidity which
is given by its momentum divided by its charge. All particles with the same rigidity follow a
track with the same curvature in a given magnetic field. For each point inside themagnetosphere and each direction from that point, there exist a rigidity threshold below
which the cosmic particles are not able to reach this point. This rigidity is called thegeomagnetic cut-off rigidity and is proportional to the magnetic field component
perpendicular to the direction of particle motion. For a particle moving towards the centre ofEarth, for example, the cut-off rigidity has a maximum value at the equator, since the particle
moves perpendicular to the field lines and the cut-off rigidity vanishes at the pole, since theparticle moves in the direction of the field lines. Therefore, geomagnetic shielding is lesseffective for high inclination orbits than for low inclination orbits. This means that in low
inclination orbits, only particles of high energy have access. Towards higher inclinations,additional particles of lower energies are observed. For a geomagnetic latitude λ, the vertical
cut-off rigidity Rc can be calculated approximately by Rc = 14.9 cos4λ/(r/re)2, where r/re is theratio of the distance r from the dipole centre to the Earth radius, re. The rigidity for particles
arriving from other directions than vertical is dependent from the angle of incidence. Due tolatitude dependent shielding, the number of particles incident in the altitude of orbiting
spacecraft increases from lower inclinations towards higher inclinations.
(49) In LEO, as well as in aviation heights, a second shielding mechanism has to beincorporated into the transport of the primary GCR or SPE ions. Whereas the geomagnetic
field on the one hand is responsible for the added radiation exposure in LEO from trappedradiation, it also causes a quite substantial reduction of radiation exposure, at least near thegeomagnetic equator (which differs from the geographic equator). This stems from the34

DRAFT REPORT FOR CONSULTATION
1205
1206
1207

1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222

deflection due to the Lorentz force of charged particles by the geomagnetic field as illustrated
in Fig. 2.12.

Fig.Fig.
2.12.
2.121983).

Deflection and trapping of charged particles by the geomagnetic field (Spjeldvik et al.,(50) Figure 2.13 provides a global map of the vertical cut-off rigidities for thegeomagnetic field model of Epoch 2000 (Smart et al., 2008). For a homogeneous dipole field,
the iso-rigidity lines would be parallel to the (geomagnetic) equator. The marked asymmetry
with a peak above 17 GV of the cut-off rigidity at the Indian Ocean (long. 90E, lat: 10N)
reflects the offset from the geographic centre of the magnetic centre by about 450 km in thisdirection. At the opposite side, in the South Atlantic this offset results in the corresponding
subsidence of the lower fringes of the inner proton belt creating thereby the so called South
Atlantic Anomaly (SAA). This is the reason for the already mentioned fact that the bulk ofradiation exposure in most LEOs is accumulated in this region.

35

DRAFT REPORT FOR CONSULTATION

1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235

Fig. 2.13Map of vertical cut-off rigidities in GV for the geomagnetic field model of Epoch 2000
Fig. 2.13.
(Smart et al., 2008).

(51) For a given orbit, the shielding due to this effect is expressed by the geomagnetictransmission factor which specifies the fraction of the GCR or solar particle fluence rate of agiven particle energy (or momentum given in units of GeVc-1) which has access to this orbit
or by the cut-off rigidity probability which specifies the probability that a particle with agiven rigidity reaches that orbit. Figure 2.14 (a) demonstrates the dependence of thegeomagnetic shielding on the orbit inclination for a circular orbit at 223 km altitude. For an
orbit of 28.5 degrees inclination which for a large fraction evades the SAA, on the average
the GCR with a momentum below about 4.2 GeV c-1 do not reach that flight route.

36

DRAFT REPORT FOR CONSULTATION
1236
Spectral particle radiance / (m2 s sr MeV/u)-1

1.0

Cut-off probability

0.8

0.6

0.4

0.2

0.0

1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263

(a)

0

4

8

Rigidity / GV

12

16

Fe

Outer space

10-3

Elliptical orbit

51.8°

10-4

I = 40°10-5
I = 30°
20°

10-6

10°
0°

10-7

102

103

104

Particle energy / MeV u-1(b)Fig. 2.14. (a) Cut-off rigidity probability for different inclination for a circular orbit of 223 km(Heinrich et al., 1979).
(b) Energy spectra of iron nuclei for outer space and for orbits in 223 km altitude of different
inclinations (Heinrich et al., 1979).

(52) For a 45 degree inclination, this momentum threshold drops to about 1.1GeV c-1,
whereas for polar orbits at least 20% of particles with the lowest energies always have accessto this altitude. On the other hand the shielding effect vanishes for ions with a momentum
above about 15GeVc-1, where at any inclination all charged ions reach this orbit. Figure 14(b) shows the influence of the magnetic shielding on the particle spectra, e.g. for Fe, which
varies strongly with the different inclination. The functions in Fig. 2.14 do not, however,include the shadow effect of the Earth itself.
(53) The shadow effect of the Earth for the Hubble Space Telescope (HST) at 28.5
degree inclination reduces the fluence rate of even the most energetic GCR by about 30%. An
Earth observation satellite such as e.g. TERRA, on the other hand, must use a near polar orbit
and therefore can be accessed by charged particles of all energies. Its higher altitude alsoslightly reduces the shielding by the Earth shadow. The high inclination of the International
Space Station (ISS) of 51.6 degree makes this manned spacecraft accessible to SPE ions of
100 MeV/u or above. This is particularly important, since in case of geomagnetic
disturbances which often accompany solar events, this geomagnetic shielding is further
reduced. Fig. 2.15 demonstrates this loss of geomagnetic shielding for the ISS for storms as
characterized by the Kp index of global geomagnetic activity (see:http://isgi.cetp.ipsl.fr/des_kp_ind.html) which can vary between 0 and 9. Under conditions ofsuch storms a much larger fraction of SPE ions can reach the orbit of the ISS.

37

Transmission factor

DRAFT REPORT FOR CONSULTATION

1264
1265
1266
1267
1268
1269

disturbed

quiet

0

Magnetic rigidity / GV
Fig. 2.15
Fig. 2.15. Calculated
geomagnetic transmission functions for the ISS orbit versus magnetic rigidity
for a quiet time geomagnetic field (dotted line) (IAGA, 1992) and for disturbed geomagnetic
conditions (solid lines) as expressed by the Kp index (Nymmik, 1999). The crosses are the resultsfrom Boberg et al. (1993) for Kp = 5.

38

DRAFT REPORT FOR CONSULTATION
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312

3.

QUANTITIES USED IN RADIOLOGICAL PROTECTION(54) The description and quantification of exposure of humans to ionising radiation needs
the definition of specific quantities and units. For many years this has been performed by
ICRU and ICRP and the actual definitions can be found in their publications (ICRU, 1993;2011 and ICRP, 2007). Human exposure to ionising radiation can occur from radiation
incident on the human body (external exposure) or from radionuclides incorporated in the
body (internal exposure). For exposure of astronauts in space, internal exposure is of very
little relevance and therefore this chapter concentrates on the concept of quantities relevant
for external radiation exposure.
(55) In the past, the definition of the specific quantities for radiological protection has
mainly considered occupational and public exposure situations on Earth concentrating on
human exposures by photons, electrons and neutrons, and also α-particles in internal
exposure. In addition, the protection quantities are defined for application in situations of low
dose and low dose rates. Limits are given in terms of these quantities in order to limit theprobability of the occurrence of stochastic detriments to humans to an acceptable level and to
avoid deterministic effects (tissue reactions).
(56) The exposure situation in space is different from that on Earth mainly due to thestrong differences in the radiation fields (see Chapter 2) and to the higher environmental dose
rate in space than on Earth whereby the likelihood of stochastic effects are increased anddeterministic effects cannot be excluded. The high contribution of heavy ions in GCR andsecondary radiation to doses in the human body needs to be considered in particular.
(57) The consequences for the definition of appropriate radiation protection quantities foruse in space situations are considered in the following sections. Organizations active in space
missions have defined detailed procedures for the assessment of human exposure in spacesince long time (see e.g. NCRP 2000; 2002). In principle, they are interested not only in thedetermination of individual doses, but in the assessment of individual radiation risks basedon such doses and this has some consequences for the definition of dose quantities. The
astronauts can be treated as single persons, or as members of small groups. Information on
sex and age can be applied and better information on the astronaut’s organ size and shapemight be available, and there may be the possibility of applying individual sensitivity factors
to the assessed organ doses if specific individual risks need to be determined (Atwell, 1994;
Bahadori et al., 2011; Bahadori et al., 2012).
3.1

Dose quantities in radiological protection(58) In radiological protection, the system of dose quantities defined by ICRP and ICRU(ICRP, 1991; ICRP, 2007; ICRU, 1993) and generally used in situations on Earth and inusual aviation altitudes includes protection quantities and operational quantities. Protection
quantities (e.g. equivalent dose in an organ or tissue, effective dose) are based on mean
absorbed doses to the organs and tissues of the human body and can be related to the risks ofionising radiation exposure. The ICRP system of protection quantities is shown in Fig. 3.1(ICRP, 2007).

39

DRAFT REPORT FOR CONSULTATION

Absorbed dose, D
Phantoms, models andindividual information
at higher doses

Mean absorbed dose, DT,R
in an organ or tissue T

Radiation-weighting
factor, wR

Equivalent dose, HTin an organ or tissue T
Sex averaging

Tissue-weighting
factor, wT

Effective dose, E

1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325

Fig. 3.1

Fig. 3.1. Dose quantities for radiological protection (protection quantities) recommended by theCommission (ICRP, 2007).

(59) Operational quantities (e.g. ambient dose equivalent or personal dose equivalent) aredefined for use in measurements which often enable an assessment of effective dose or meandoses in organs or tissues of humans which are generally not measurable.
(60) In radiation biology, clinical radiology, and radiological protection the absorbed
dose, D, is the fundamental physical dose quantity. It is used for all types of ionising radiation
and any irradiation geometry.
(61) Absorbed dose, D, is defined as the quotient of d by dm, where d is the meanenergy, imparted by ionising radiation to matter of mass dm, thus
D

1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341

d
.
dm

(3.1)

The SI unit is J kg-1 and its special name is gray (Gy). Absorbed dose takes account of theradiation field inside and outside the specified volume of mass dm and hence of all charged
particles which were produced in or enter that volume. Its value is derived from the meanvalue of the stochastic quantity of energy imparted, ε, and does not reflect the random
fluctuations of the interaction events in tissue. Generally, absorbed dose is a measurable
quantity and primary standards exist to allow its determination by measurement.
3.1.1 Protection quantities(62) Generally, radiological protection is concerned with controlling exposures toionising radiation so that tissue reactions are prevented and the detriment from stochastic
effects is limited to accepted levels. The fundamental protection quantities are based on
absorbed doses imparted to organs and tissues of the human body. These quantities aredesigned to allow quantification of the exposure to ionising radiation from both whole andpartial body irradiation (ICRP, 1991; 2007). The estimated doses can then be compared with40

DRAFT REPORT FOR CONSULTATION
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352

recommended dose limits for e.g. occupationally exposed people or at higher doses mean
absorbed doses in organs and tissues may be used for the assessment of risk of cancer orother detriments.
(63) Mean absorbed dose in an organ or tissue In radiological protection, the maininterest is not directed to the absorbed dose at a point in the human body, but to the absorbed
dose averaged over a tissue or organ volume. The mean absorbed dose, DT,R , in an organ or
tissue T due to a radiation of type R is the basic quantity for the definition of the protection
quantities equivalent dose and effective dose used for describing exposures at low doses anddose rates where stochastic effects are dominant. In a mixed radiation field the mean
absorbed dose, DT, in an organ or tissue T is given byDT   DT, R .

(3.2)

R

1353
1354
1355
1356
1357
1358
1359
1360

(64) The mean absorbed dose is not always representative of the local absorbed dosethroughout an organ or tissue, e. g. for low-penetrating radiation. For strongly-penetratingradiation, however, the absorbed dose distribution within most organs may be sufficiently
homogeneous and thus the mean absorbed dose is mostly a suitable measure of the dosethroughout the organ or tissue.
(65) Equivalent dose in an organ or tissue The protection quantity equivalent dose inan organ or tissue, HT, is defined by
H T   wR DT, R

(3.3)

R

1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371

where wR is the radiation weighting factor for radiation R which considers the differences in
the radiobiological effectiveness of different radiations (details see Section 3.2.2) and DT,R
the average absorbed dose in the volume of a specified organ or tissue, T, due to the radiationof type R. The radiation R is given by the type and in the case of neutrons the energy ofradiation either incident on the body or emitted by radionuclides residing within the body.
The sum is performed over all types of radiations involved. The unit of equivalent dose is J
M
F
kg-1 and has the special name sievert (Sv). Equivalent doses, H T and H T , are specified inmale and female bodies represented by male and female reference voxel phantoms.
(66) Effective dose The effective dose, E, introduced in Publication 60 (ICRP, 1991) andagain defined in Publication 103 (ICRP, 2007) as:E   wT H T

(3.4)

T

1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383

where wT is the tissue weighting factor for organ or tissue T representing the relative
contribution of that organ or tissue to the total health detriment resulting from uniform
irradiation of the body at low doses and dose rates. It is Σ wT = 1. The sum is performed over
14 organs and tissues of the human body individually considered in the definition of E andfor which specific wT values are given in Table 3.1 and an additional remainder tissue
representing a mean value of further tissues (14 tissues, but only 13 tissues for each gender)(see Table 3.1).
(67) The unit of effective dose is J kg-1 with the special name sievert (Sv). The same unit
is also used for the operational dose quantities. Care must be taken in ensuring that thequantities being used are clearly stated.
(68) In the calculation of effective dose the equivalent doses HT are taken as the meanvalues averaged over the male and female organs and tissues:

41

DRAFT REPORT FOR CONSULTATIONH T  0.5( H TM  H TF ).

1384

(3.5)

1385
1386
1387
1388
1389
1390

(69) The concept of tissue weighting factors has been introduced already in 1977 (ICRP,
1977), extended in 1991 (ICRP, 1991) and further modified in 2007 (ICRP, 2007). The
values of wT for the specified tissues and organs are based on the detriment due to stochastic
effects after radiation exposure and on judgments. They represent mean values for humans
averaged over all ages and both sexes.

1391

Table 3.1. Tissue weighting factors, wT (ICRP, 2007)

1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422

Organ/Tissue

wT

Total
Contribution

Lung, Stomach, Colon, Bone marrow, Breast,
Remainder

0.12

0.72

Gonads0.08

0.08

Thyroid, Oesophagus, Bladder, Liver

0.04

0.16

Bone surface, Skin, Brain, Salivary glands

0.01

0.04

Notes:
1. The wT for gonads is applied to the mean of the doses to testes and ovaries.
2. The dose to the colon is taken to be the mass-weighted mean of ULI and LLI doses, as in the Publication 60 formulation.
The specified remainder tissues (14 in total, 13 in each sex) are: Adrenals, Extrathoracic tissue (ET), Gall bladder,
Heart, Kidneys, Lymphatic nodes, Muscle, Oral mucosa, Pancreas, Prostate(♂), Small intestine (SI), Spleen, Thymus,
Uterus/cervix (♀).

(70) The use of effective dose allows exposures in very different situations (e.g. internaland external exposure by different types of radiation and inhomogeneous exposures of thebody) to be combined and results in a single dose value which considerably simplifies the
specification of exposure limits. Effective dose, however, is not designed as a quantity
considering individual properties of a specific person and should, therefore, not be applied foran assessment of radiations risks of a single person.
3.1.2 Operational dose quantities(71) The protection quantities defined by mean organ or tissue doses in the human bodyare not measurable in practice and, therefore, cannot be used as quantities in radiation
monitoring. For radiation measurements in situations of external exposure (area or individual
monitoring) specific operational dose quantities have been defined by ICRU (ICRU 1985;
1988; 1993; 2001). In monitoring at low doses the values of these quantities are taken as
sufficiently accurate assessments of effective dose or skin dose, respectively, if their values
are below the recommended limits for occupational exposure.
(72) The basis for the definition of the operational quantities is the quantity dose
equivalent, H, defined by
H=QD

(3.6)

where D is the absorbed dose at the point of interest in tissue and Q the corresponding meanquality factor due to the charged particles at that point.
(73) For the different tasks of monitoring of external exposures the following scheme canbe used for describing the application of the different operational dose quantities (ICRP,
2007)
42

DRAFT REPORT FOR CONSULTATION
1423
1424
Task

1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458

Operational dose quantities forarea monitoring

individual monitoring

Control of effective
dose

ambient dose equivalent,H*(10)

personal dose equivalent,Hp(10)

Control of doses to theskin, the hands and feet

directional dose equivalent,H’(0.07, Ω)personal dose equivalent,Hp(0.07)

Control of doses to thethe lens of the eye

directional dose equivalent,H’(3, Ω)personal dose equivalent,Hp(3)(74) The operational quantities for area monitoring at a location in a radiation field aredefined by the dose equivalent at a point in a simple phantom, the ICRU sphere. It is a sphereof tissue-equivalent material (30 cm in diameter, ICRU (soft) tissue with density: 1 g cm -3,
and mass composition: 76.2 % oxygen, 11.1 % carbon, 10.1 % hydrogen and 2.6 % nitrogen).
These quantities are defined to be point quantities fulfilling the condition of being additive
with respect to the different components of the radiation field at the point of interest. For its
definition the terms “expanded” and “aligned” radiation field are introduced (see Glossary)and the value of the quantity is given by the dose in a point at a fixed depth in the sphere. The
sphere is hypothetical, a mathematical construct for the determination of the values of thequantities for area monitoring.
Ambient dose equivalent, H*(10)(75) For area monitoring the operational quantity for assessing effective dose is theambient dose equivalent, H*(10), defined by (ICRU 2001):
The ambient dose equivalent, H*(10), at a point in a radiation field, is the dose equivalentthat would be produced by the corresponding expanded and aligned field in the ICRU
sphere at a depth of 10 mm on the radius vector opposing the direction of the aligned field.
(76) In most practical situations on Earth ambient dose equivalent provides aconservative estimate of effective dose a person would receive at that position. This,
however, may not be the case for persons in high energy radiation fields, e.g. in cosmic
radiation fields (Pelliccioni, 1998).
Directional dose equivalent, H'(d, )(77) For area monitoring the quantity for assessing the dose to the skin and theextremities (hands, arms, feet) and the dose to the lens of the eye, the operational quantity is
the directional dose equivalent, H'(d, ) defined by:
The directional dose equivalent, H'(d,), at a point in a radiation field, is the dose
equivalent that would be produced by the corresponding expanded field in the ICRU
sphere at a depth, d, on a radius in a specified direction, .
(78) For assessing the dose to the skin and the extremities d = 0.07 mm is used andH'(d,) is then written H'(0.07,). In case of monitoring the dose to the lens of the eye thequantity H'(3,) with d = 3 mm was recommended by ICRU.

43

DRAFT REPORT FOR CONSULTATION
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505

Personal dose equivalent, Hp(d)(79) Individual monitoring of external exposure is usually performed with personal
dosemeters worn on the body and the operational quantity defined for this application takes
this situation into account. For individual monitoring the operational quantity is the personaldose equivalent, Hp(d).
The personal dose equivalent, Hp(d), is the dose equivalent in ICRU (soft) tissue (seeSection 4.3) at an appropriate depth, d, below a specified point on the human body.
(80) The specified point is usually given by the position where the personal dosemeter isworn. For the assessment of effective dose a depth d = 10 mm and for assessing equivalentdose to the skin and to the hands and feet a depth d = 0.07 mm is recommended. In special
cases of monitoring the dose to the lens of the eye a depth d = 3 mm has been proposed to beappropriate.
3.2

Description of radiation quality(81) The biological effectiveness of ionising radiation with respect to the induction ofcancer or other tissue reactions in the human body and of hereditary effects depends on thetype and energy of the radiation, on the tissue type exposed, on the dose and dose rate applied
to the tissue and on the detriment considered. The induced effects differ also in the latency
time between the exposure and the occurrence of the effects.
(82) In radiological protection the effectiveness at low doses and dose rates are mainly ofinterest. For these doses and dose rates the stochastic effects - cancer induction and hereditaryeffects - are important and the standard approach in radiological protection is that the shapeof the dose-response relationship at low doses and dose rates is based on the model that theprobability of a stochastic effect is proportional to the applied dose (linear-non-thresholdmodel (LNT)) (ICRP, 2005).
(83) At higher doses, however, when non-stochastic effects (deterministic effects, tissue
reactions) may occur, LNT is not an acceptable approximation. Tissue reactions occur always
above a dose threshold. The threshold dose value depends on the type of the tissue reaction
and is mostly above an applied absorbed dose of 0.5 - 2 Gy.
(84) In principle, for risk estimates from exposure by different types of ionising radiation,
the absolute values of biological effectiveness of radiation with respect to the induced effectneed to be known. The mostly used procedure of taking care of the differences in the
biological effectiveness, however, is to use risk factors for a reference radiation (usually
photons) and to consider the differences of other types of radiation by applying a factor
relative biological effectiveness (RBE) which has already been introduced by Failla andHenshaw in 1931 (Failla et al., 1931) and is discussed in detail in ICRP Publication 92(ICRP, 2003). While RBE-values always depend on the biological endpoint considered andon dose and dose rate applied, for the definition of quantities in radiological protection asingle set of radiation weighting factors and radiation quality factors has been chosen (ICRP,
2007) based on data at low doses and dose rates. This is further discussed in the next sections.
3.2.1 Relative biological effectiveness(85) In radiobiology the differences in the effectiveness of the different ionisingradiations have led to the definition of the relative biological effectiveness (RBE). RBE
values are given as the ratio of the absorbed doses of two types of radiation producing the44

DRAFT REPORT FOR CONSULTATION
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553

same specified biological effect under identical irradiation conditions (dose value of areference radiation divided by the corresponding dose value of the considered radiation at thesame level of the specified biological effect). RBE values depend on the conditions of
exposure including the biological effect investigated, the tissue or cell type exposed, the doseand dose rate, and the dose fractionation scheme. Therefore, for a given type of radiation,
experimental investigations often provide a large range of RBE values (ICRP, 2003). As thebasis for selecting radiation weighting factors (see 3.2.2), RBE values with respect tostochastic effects (cancer induction and hereditary effects) are of main interest. Usually RBEvalues increases with decreasing dose and dose rate and are believed to reach maximum
values (RBEM) at low doses and low dose rates. RBEM-values are most relevant forradiological protection applications. In ICRP Publication 92 (2003), different methods are
discussed to determine RBEM at low doses and dose rates. The discussion includes various
types of high-LET radiation, e.g. protons, neutrons and -particles. For heavy ions, however,very limited data were available at that time.
(86) Generally, low-LET radiation is taken as reference radiation, mostly high-energy xrays or -rays from 60Co or 137Cs. There are, however, substantial differences in the biologicaleffectiveness of photons of different energy (Schmidt et al., 2002). Nevertheless, there exists
no international recommendation on defining a specific photon source as a general reference
radiation. This has the consequence that a broad range of experimental data with photons has
been used as a basis for the definition of radiation weighting and quality factors (ICRP,
2003).
(87) While on the one hand RBEM-values are the basis for the definition of radiation
weighting factors and the Q(L)-function, on the other hand, RBE-values are used for theassessment of radiation risks from human exposures by different types end energies ofradiation. A risk factor for the radiation and tissue of interest is obtained by multiplying therisk factor for the reference radiation, e.g. photons, by the corresponding RBE-value. An
uncertainty for risk assessment, however, comes in, because RBE-values are often
determined by investigating biological effects in single cells or small animals at higher doses,
while radiation risks are assessed for stochastic effects, e.g. cancer induction and hereditaryeffects, in humans.
(88) The biological effectiveness of ionising radiation is known to be correlated with its
energy deposition properties along the tracks of charged particles, especially with theionisation density along their tracks. For applications in radiological protection, the complex
structure of the charged particle tracks in tissue is characterized by a single parameter only,
the unrestricted linear energy transfer, L∞, (often denoted linear energy transfer, LET or L).
Unrestricted linear energy transfer, L means that the transfer energy includes the energies ofall emitted δ-electrons independent of their range, while restricted LET, L, means that only-electrons with energies of less than  are considered. In general, LET is not simply related
to the biological effectiveness because, for example, ions of different Z show different
effectiveness at the same LET-value (Cucinotta et al., 2000a).
(89) The study of the LET-dependence of RBE is concentrated on the study of radiation
effects in single cells by irradiating thin cell samples with charged particles of various types
and energies. In animal experiments, however, with long ranges of charged particles in thetissue, the LET-dependence of an effect, e.g. cancer induction, is more difficult to study.
(90) While for neutrons and alpha particles a broad range of experimental data to manydifferent biological endpoints exists including data from animals (NCRP, 1990; ICRP, 2003),
the situation for high-energy charged particles is more problematic. Epidemiological data on
cancer induction in humans from exposure to high-energy particles and heavy ions are not
45

DRAFT REPORT FOR CONSULTATION
available and experimental data on cancer induction in animals are scarce (ICRP, 2003).
Most RBE data for high-energy protons and heavy ions have been obtained by experimentswith cells at high doses (> 1Gy) and high dose rates which are of particular interest forheavy-ion radiotherapy applications (Taucher-Scholz et al., 1999, George et al., 2003,
Durante, 2002) with only a few studies of tumors in mice (Fry et al., 1985, Alpen et al., 1993,
Weil et al., 2009).
(91) Experimental data of RBE versus LET have been obtained for various biological
endpoints. The general shape of the RBE-LET relationship is always similar. At low LETvalues there is an increase in RBE with increasing LET up to about 100 to 150 keV/μm andfor higher LET-values, RBE decreases with increasing LET. Figures 3.2 to 3.4 show sometypical examples of RBE-LET relationships obtained for different biological endpoints.

RBEM

1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565

1566
1567
1568
1569

LET / keV mm-1
Fig. 3.2. RBEM versus LET for oncogene transformations in C3H10T1/2 cells of embryos of mice
(Brenner et al., 1992).
Fig. 3.2

46

DRAFT REPORT FOR CONSULTATION
1570
1571
100

RBEM

10

1

0.1
10

100

1000

10 000100 000

LET / keV mm-1
1572
1573
1574
1575
1576

1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588

Fig. 3.3. RBEM versus LET for the induction of mutations at the hprt locus in Chinese hamster V79
cells. DataFig.
are3.3from Kiefer et al. (1999, 2001). The dotted line shows the Q(L) function as defined in
ICRP Publication 60 (ICRP, 1991).

Fig. 3.4. RBEM versus LET for total chromosomal exchanges measured within the first cell cycle
Fig.the3.4 premature chromosome condensation (PCC) method (George et al., 2007, Cucinotta et al.,using
2008). The line shows the Q(L) function as defined in ICRP Publication 60 (ICRP, 1991).

(92) In general, the biological effectiveness is not simply related to LET, especially forheavy ions with high LET-values. This is because the width of a particle track depends on thevelocity of the particles. Particles of different Z show different effectiveness at the same
LET-value (Cucinotta et al., 2011). The position of the peak RBE versus LET depends onparticle charge number and does not occur at a fixed LET (see Figs. 3.5 and 3.6). The peak
position changes from less than 100 keV/mm to more than 150 keV/mm as Z increases fromprotons with Z=1 to Fe with Z=26. RBE depends on charge Z and energy E of the particle,
47

DRAFT REPORT FOR CONSULTATION
1589
1590
1591
1592
1593

and not on LET alone. At a fixed value of LET less than the peak position, particles withlower Z are more biologically effective. In addition, the slope of rise of RBE with LET isvariable with the endpoint/system studied, and the slope of decrease of RBE at high LETvalues is predicted to be proportional to LET-1 rather than LET-1/2.

5

4
3
2
1

100

1594
1595
1596
1597
1598
1599

101

102
LET in keV mm-1

103

104

Fig 3.5. Relative biological effectiveness (RBE) for inactivation of V79 hamster cells (closed
symbols) and T1 mammalian cells (open symbols) exposed to beams of accelerated heavy ions (▲, ∆deuterons and He-ions; ,○ heavier ions) versus LET (Thacker et al., 1979).
Total Exchanges in Human Lymphocytes
40

Si
Fe

RBEmax

30

20

10

0
10

1600
1601
1602
1603
1604
1605
1606

100

1000

LET, keV/ m
Fig. 3.6. RBEmax versus LET for chromosomal aberrations (total exchange) of human lymphocytes
exposed to Si and Fe nuclei, relative to low-dose and dose-rate γ-rays (George et al., 2007).
.

(93) For the same LET-value the distribution of δ-rays strongly varies with the ion
considered (see Fig 3.7). The approach of describing radiation quality in terms of LET
assumes that the various ion tracks shown in Fig. 3.7 produce the same cancer risk, although48

DRAFT REPORT FOR CONSULTATION
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1612
1613

the initial physical-chemical stages are quite distinct. Hence, there is considerable support torelate RBE to a function better correlated to the track structure of the charged particles
passing tissue (Cucinotta et al., 2011), especially to the spatial distribution of δ-rays along the
tracks. Arguments from Katz (Katz, 1970; Katz et al., 1972) and observations by Goodhead
et al. (Goodhead, 1980) supports the hypothesis that especially for heavy ions biologicaleffects are strongly influenced by particle track structure including δ-ray effects rather thanby the stopping power (LET) only.
10

Y / μm

8

4He2+

12C6+

0.45 MeV/u

10 MeV/u

6
4

2

0
10
56Fe28+Y / μm8
61000 MeV/u
28Si14+90 MeV/u

4
2

0
-4

-2

0

2

4

-4

X / μm

1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631

-2

0

2

4

X / μmFig. 3.7. Simulated tracks segments for the following ions in water: 4He (0.45 MeV/u), 12C (1056
3.7 MeV/u), andMeV/u), 28SiFig.(90Fe (1 GeV/u). Shown are projections over the XY plane. Ions are
generated at the origin along the Y axis in liquid water at 25°C under identical LET conditions (~150keV μm-1). Each dot represents a radiolytic species (Plante et al., 2008).

(94) A parameter Z*2/β2, where Z* is the effective charge number of the nuclei and  thevelocity of the nuclei relative to the light velocity, has been proposed by Katz and others(Katz, 1970; Katz et al., 1972) to be a better descriptor of energy deposition in small volumes
than LET, especially for heavy ions. This is based on the idea that a reaction cross section
with respect to biological reactions in tissue should include the effect of δ-rays. A value of Z*
can be obtained by using the following equation given by Barkas (Barkas, 1963):
Z* = Z (1-exp(-125  Z2/3))(3.7)

where Z is the charge number of the nuclei considered. As an example Figure 3.8 shows
calculations comparing the frequency of energy deposition above 300 eV in a volume ofabout the size of a nucleosome. Obviously the parameter Z*2/β2 provides an improved
descriptor of energy deposition in small volumes compared to LET.

49

DRAFT REPORT FOR CONSULTATION

F(>300 eV) per cell / Gy-1

1632
100
80


― ― ―― ― ―– – – –ProtonHeliumSilicon
Iron

10

100

60
40
20
0

1

10

100

1000 1

LET / keV mm-1
1633
1634
1635
1636
1637
1638
1639
1640
1641

1000 10000

Z*2 / 2

Fig. 3.8. Number of nucleosomes per cell receiving 300 eV or more as a function of LET (left) or
Z*2/β2 (right). Calculated data are shown for H, He, Si, and Fe nuclei (Cucinotta, 2011).
Fig. 3.8(95) As a consequence, a RBE function has been derived and described to be dependent
on two parameters of the particle, either given by E and Z, or alternatively by Z*2/β2(Cucinotta et al., 2011). In Fig. 3.9 the same RBE data as shown in Fig. 3.5 are plottedagainst Z*2/β2 and this plot may be a better basis for defining a quality factor function thanusing the LET parameter.
5

4
3
2
1

101

1642
1643
1644
1645
1646
1647
1648
1649
1650
1651

102

103

104

105

Z*2 / 2
Fig 3.9. Relative biological effectiveness (RBE) for inactivation of V79 hamster cells (closed
symbols) and T1 mammalian cells (open symbols) exposed to beams of accelerated heavy ions (▲, ∆deuterons and He-ions; ,○ heavier ions) versus (Z*/)2 (Thacker et al., 1979).

3.2.2 Radiation weighting factor(96)
Radiation weighting factors, wR, have been used in the definition of the protection
quantity equivalent dose in an organ or tissue in ICRP Publication 60 (ICRP 1991) andnumerically modified in Publication 103 (ICRP, 2007). Values of wR are given for various

50

DRAFT REPORT FOR CONSULTATION
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1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666

types of radiation either incident on the human body or emitted by radionuclides in the body.
Data for wR are given in Table 3.2. The same values of the radiation weighting factors areapplied to all tissues and organs of the body independent of the degradation of the primaryradiation and the production of secondary radiations of different radiation quality. It may beseen as a mean factor representing radiation quality averaged over the different tissues andorgans of the body. The application of wR-values is restricted to low doses and dose rates andshould not be applied in cases of higher doses where tissue reactions may occur.
(97)
Except for neutrons, all types of particles are given a single weighting factor value.
This simplification is seen to provide sufficient precision for general applications inradiological protection, even if it is well known that radiation quality depends also on theenergy of the particle involved. This is especially the case for heavy ions of high energies
which, however, in most radiation fields at the Earth are less important of radiologicalprotection.
Table 3.2. Radiation weighting factors1, wR (ICRP, 2007)
Radiation type
Photons

1

Electrons and muons

1

Protons and charged pions

2

Alpha particles, fission
fragments, heavy ions20

Neutrons

1667
1668
1669
1670
1671

Radiation weighting factor, wR

A continuous curve as a function ofneutron energy(see equation 3.9 and Fig. 3.2)

(1) All values relate to the radiation incident on the body or, for internal sources, emitted
from the source.

(98)
For neutrons the following function is recommended for the calculation ofradiation weighting factors (ICRP, 2007):
(3.8)

1672
1673
1674

where the neutron energy, En, is given in MeV (see also Fig. 3.10).

51

DRAFT REPORT FOR CONSULTATION

1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705

Fig. 3.10.

Radiation weighting factor, wR, for neutrons versus neutron energy (ICRP, 2007).

(99)
For applications in space, where high-energy heavy ions significantly contributeto the total dose in the human body, a more realistic approach for radiation weighting should
be chosen (ICRP, 2007). This could, for example, be based on the calculation of mean quality
factors in the human body (see Section 3.2.3). Some other difficulties with the wR-concept for
application in high energy radiation fields have also been discussed by Pelliccioni (1998).
3.2.3 Quality factor(100) Radiation quality is seen to be strongly correlated with its energy deposition
properties along the tracks of charged particles, especially with the ionisation density along
their tracks. For applications in radiological protection, the different biological effectivenessof radiation is considered by introducing the quality factor function, Q(L). Q(L) characterizes
the biological effectiveness of a charged particle with a linear energy transfer L at a point ofinterest in tissue relative to the effectiveness of a reference radiation at this point. Q isdefined by a function of L in water (not in tissue) as given in various publications of ICRP
and ICRU (ICRP, 1963, 1977, 1991; ICRU, 1970, 1986). RBE-values provide the basis forthe selection of a quality factor function used in the definition of the specific dose quantities
in radiological protection (see Section 3.2). For this application, all photons and electrons (alllow-LET radiation with L<10 keV/μm) are weighted by Q = 1. This is seen to be an
approximation sufficient for usual radiation protection applications and greatly simplifies
measurements and calculations.
(101) The actual quality factor function Q(L) with L for charged particles in water was
given in Publication 60 (ICRP, 1991):

Q(L) =

1
0.32 L – 2.2
300 / LL < 10 keV/mm
10 keV/mm  L  100 keV/mm
L > 100 keV/mm

52

(3.9)

DRAFT REPORT FOR CONSULTATION
1706
1707
1708
1709
1710
1711

(102) The Q(L) function is the outcome of radiobiological investigations on cellular andmolecular systems as well as on the results of animal experiments (see e. g. (ICRP, 2003))
and has not been changed since 1990. The function includes, however, also some judgments
for simplifying radiological protection practice. Q(L) = 1 for L<10keV/mm, even it is wellknown that the RBE of photons increases with decreasing energy (ICRP, 2003).
(103) The quality factor Q at a point in tissue is then given by:
L 

Q

1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726

(3.10)

where D is the absorbed dose in tissue and DL = dD/dL the distribution of D in L (forcharged particles in water) at the point of interest in tissue.
(104) For exposure of the human body by neutrons the radiation field is modified in the
body by moderation of the incident neutrons and secondary radiation from neutron reactions.
Therefore, for a given neutron exposure situation, the value of the quality factor depends on
the position in the body and the mean radiation quality factor in organs and tissues of the
body may differ. For each organ or tissue T, a tissue-mean radiation quality factor, QT , canbe calculated using:QT 

1Q( L)DL dLdm
mT DT mT L(3.11)

where mT is the mass of the organ or tissue T. A body-mean quality factor, QE, averaged overthe human body by considering the mean organ absorbed doses, DT, and the tissue weighting
factors, wT, is given by

QE   wT QT DT /  w T D T .
T

1727
1728
1729
1730
1731
1732
1733
1734

1
Q( L) DL dL
D L0(3.12)

T(105) Figure 3.11 shows both the radiation weighting factor and the body-mean quality
factor, QE,AP, calculated for the adult male reference phantom, for monoenergetic neutrons(AP incidence) versus neutron energy. Values of QE are similar for other directions ofneutron incidence (e.g. ISO). Obviously stronger differences between wR and QE are only forneutron energies between 0.1MeV and 10MeV. For neutron energies above 10MeV, thedifference is negligible. Differences between QT for a single organ and wR may be, however,much larger.

53

DRAFT REPORT FOR CONSULTATION
1735

1736
1737
1738
1739
1740
1741

1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752

Fig. 3.11. Radiation weighting factor, wR, and body-averaged mean quality factor, QE,AP, calculated
for neutrons (AP incidence) versus neutron energy (Sato et al., 2009).

(106) Similar calculations have been performed for incident protons by Sato et al. (Sato,2009) and these data are shown in Fig. 3.12.

Fig. 3.12. Radiation weighting factor, wR, and body-averaged mean quality factor, QE,AP, calculated
for protons (AP incidence) versus proton energy (Sato et al., 2009).

(107) While for energies of incident protons below about 10 MeV there are large
differences between the radiation weighting factor and the mean quality factor, they are much
lower at higher proton energies and are less than 20% at proton energies above 1 GeV.
Protons below about 10 MeV, however, are low-penetrating radiation which are mostly
stopped already in the skin of exposed persons and hence contribute little to the effective
dose in cosmic radiation fields with many protons of high energies. When exposure of theskin needs special attention, protons below about 10 MeV, however, need also to be
54

DRAFT REPORT FOR CONSULTATION
1753
1754
1755
1756
1757
1758
1759
1760

1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785

considered. In such cases, the absorbed dose to the skin, and not the effective dose is of prime
interest.
(108) At proton energies above 20 MeV, the mean quality factor is always between 1 and
2. At these energies, protons can be seen to be low-LET particles. The increase of Q atenergies above 150MeV is due to proton reactions in tissue where secondary charged
particles are produced.
(109) While for high-energy neutrons and protons the difference between wR and the meanquality factor is relatively small, the situation is quite different for heavy ions.

Particle energy / MeV u-1

Fig. 3.13. Radiation weighting factor, wR, and body-averaged quality factors, QE,ISO, for 4He, 12C,
24
56
MgFig.and
3.13 Fe (ISO incidence) versus particle energy (Sato et al., 2010).

(110) The body-mean quality factor is strongly varying with the type and energy of the ion(Sato et al., 2010), while the wR-value has been fixed to 20 for all heavy ions and all energies.
For example, Fig. 3.13 shows body-mean values of QE for 4He, 12C, 24Mg and 56Fe ions withisotropic radiation incidence to the body. The value varies between about 2 and 24 dependingon the ion type and the energy. There are also stronger variations in QT depending on theposition of the organ or tissue in the human body. This situation underlines the decision, notto select a single radiation weighting factor value for all heavy ions and all particle energies.
The recommended concept of quantities for use in radiological protection of astronauts inspace takes account of this fact (see Section 3.3.1).
(111) Similar to the dependence of RBE for high-energy ions, a different way of defining
a quality factor function may be derived from the track structure of the charged particles
rather than being only related to LET. Cucinotta et al. (Cucinotta, 2011a) have proposed afunctional dependence of a quality factor on two parameters of the particle, Z and E oralternatively can be expressed in terms of Z*2 / β2 and LET. Because the RBE values for an
induction of leukaemia and of solid cancers are quite different, they proposed two different
functions Q(Z,E) for leukaemia and solid cancers (see Fig. 3.14).
(112) The general ideas discussed on track-structure models have been used to define across section function related to risk which may be written aswithΣ(Z, E) = Σ0 P(Z, E) + ( L / 6.24) (1 – P(Z, E))(3.13)

P(Z, E) = (1 – exp(–Z*2 / 2))m(3.14)

55

DRAFT REPORT FOR CONSULTATION
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819

where Σ0, m, and  are parameters which should be based on fits to data from radiobiology
experiments, and the low-LET slope, , estimated from epidemiological data for radiations. The parameter  is the particle velocity relative to the velocity of light. Z* is theeffective charge number which includes a velocity dependent correction to Z at low particle
energies (Barkas, 1963) as defined in eq. (3.7).
Using the equations above, a quality factor function, Q(Z,E) can then be defined by
Q(Z,E) = (1 – P(Z, E) + (6.25 (Σ0/( L)) P(Z, E)(3.15)(113) Note that L is not an independent variable in addition to Z and E, but for a given Z
and E, the L-value is fixed. Alternatively, one may write Q(Z,L) or also Q(E,Z*2/ 2). At highparticle energies, this function defines a 1/L-dependence of Q different from the 1/L1/2dependence given by the Q(L) function of eq. (3.10). The interpretation of the parameters isquite general, and is not tied to a particular track structure models per se, but rather is anefficient parameterization of radiobiology data for particles. The parameters can be describedas follows: Σ0 is the maximum value of the cross section, which is related to RBEmax for themost biologically effective particle types, m is the slope of the cross section for increasing
ionisation density, with values m>1 necessary to have RBE>1, and  determines thesaturation value of the cross section with increasing Z*2/ 2, where the RBE begins to
decline.
(114) High-energy protons of about 150 MeV have an LET similar to -radiation and theirkinetic energy is below a value where nuclear reactions become important. Manyexperiments have shown a biological effectiveness for those protons to be very similar to radiation. For proton of this energy, it is P(Z,E) << 1, and Q ~1.
(115) For solid cancer risks, radiobiology data are sparse. However, the largest RBE for
HZE nuclei is in the range from 20 to 50 for solid tumors in rodents, and for chromosomal
aberrations and mutations in human cells. A lower value is found for leukaemia. This
assumes a linear dose response at low doses for charged particles, ignoring non-targetedeffects or other possible mechanisms which may lead to deviations from linearity. Thus, forexample, if a peak RBE value of approximately 40 is assumed for Si at 100 keV/μm where
P(Z,E) ~1, Σ0 / can be estimated as 40x100/6.24. A comparison of the quality factor basedon LET and on both, L and Z is shown below (Fig. 3.14). The influence in the uncertainties inthe values of these parameters, which describe the uncertainties in information on RBEmax
and the peak position of the RBEmax with LET for different particles can be investigatedusing Monte-Carlo methods (Cucinotta et al., 2011).

56

DRAFT REPORT FOR CONSULTATION
50

50

Protons
40

40

ICRP
NASA Solid Cancer
NASA Leukemia

30

Q

Q

30

20

20

10

10

0

0
1

10

10

100

1000

40

40

SiliconIron

ICRP
NASA Solid Cancer
NASA Leukemia

ICRP
NASA Solid Cancer
NASA Leukemia

30

Q

30

Q

100

LET, keV/mm

LET, keV/mm

20

20

10

10

0
100

0
100

1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844

ICRP
NASA Solid Cancer
NASA Leukemia

Carbon

1000

1000

10000

LET, keV/mm

LET, keV/mm

Fig. 3.14. LET dependence of the quality factor, Q, for H, C, Si, and Fe nuclei as defined by theCommission (ICRP, 1991) and as proposed by NASA (Cucinotta, 2011) differently defined forconsidering relative risks of either solid cancer or leukaemia .

3.3

Approach for space applications(116) The situation in a space vehicle is characterized by the primary radiation field
consisting of various high-energy charged particles from protons up to heavy ions such as Fe56 or even higher Z values, and by radiation components of photons, electrons, neutrons andother reaction products from the interaction of primary particles with the materials of thespacecraft (see Chapter 2). This results in many different types of radiation together withbroad energy distributions up to particle energies of many GeV/u.
(117) Individual doses are generally higher than in usual exposure situations on Earth. As
a consequence, deterministic effects in specific organs, e.g. lens of the eye or skin, cannot beignored. This needs specific consideration and will be further discussed in Sect. 3.3.3.
(118) The consequence of this specific situation is that some concepts of the quantities
used in radiological protection on Earth have to be reconsidered for use in space. For
example, the operational quantity for area monitoring of penetrating radiation which is basedon the dose equivalent at 10 mm depth of the ICRU sphere has been mainly designed on thebasis of photon and neutron data for control of effective dose and is limited in its application
to radiation with energies where secondary charged particle equilibrium is achieved at about
10 mm depth in tissue. This is not the case for very high energy particles. For this situation
computer modelling and simulation of exposure situations become very important in addition

57

DRAFT REPORT FOR CONSULTATION
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876

to of measurements.
3.3.1 Protection quantities(119) Radiation risk estimates are generally based on absorbed doses in the tissues andorgans of the human body and the concept of the mean absorbed dose, DT, in various organs
and tissues of the body (see Section 3.1.1) has been assumed to be applicable also for
astronauts in space. Limitation to this concept, however, may arise by the fact that fluence
rates of heavy ions are very low. If only few particles pass an organ with a high energy
transfer along each single particle track, averaging of the dose over an organ is a
simplification which increases the uncertainty when risk estimates are considered. Anotherproblem arises due to the large fraction of charged particles in the radiation field. Dependingon their energy, they may be stopped in the human body and hence the depth dose
distribution may not sufficiently homogenous over larger tissues or organs in the body toconsider only an averaged value. Nevertheless, the mean absorbed dose in organs or tissuesof the body is a very useful concept for radiological protection practice and for omnidirectional (isotropic) exposure of an astronaut which can often be assumed in space, thisproblem is less important.
(120) DT is a quantity which cannot be measured but is usually determined by applying
calculated conversion coefficients which relate the mean dose in an organ or tissue to an
external radiation field quantity (fluence for particles or air kerma for photons). They are,however, not calculated for any individual, but for adult male and female reference persons(ICRP, 2009) and are, therefore, restricted in the assessment of individual doses. The charged
particles in the energy range of some GeV/u which are present in space, have very longranges in tissue which results in a relatively homogeneous exposure of the human body andthe variation of the mean organ doses is not very large, especially in case of isotropic
exposure (see Section 6.3).
(121) Obviously, the general use of wR = 20 for all heavy ions does not reflect thevariation of RBE with type and energy of heavy ions and the Q-approach is better correlatedwith the assumption of a general dependence of RBE on LET and possibly on (Z*2/β2) (seeSection 3.1.3). It is, therefore, endorsed to follow the approach already applied by space
agencies and to use the term dose equivalent in an organ or tissue T, HT,Q, defined by

HT,Q = QT DT

1877
1878
1879

(3.16)

with the mean quality factor QT in an organ or tissue T for the given radiation field. Whenusing the Q(L) function, QT is calculated by
L 

QT 

1880
1881
1882

(3.17)

with the mass, mT, of the organ or tissue considered.
(122) If a quality factor is defined by a function Q(Z,E), a QT-value can be calculated by

QT 

1883
1884

1
Q( L) DL dLdm
mT DT mT L01
( Q( Z , E ) DE ( Z , E )dEdm
mT DT mT Z E

or alternatively

58.

(3.18a)DRAFT REPORT FOR CONSULTATION
QT 

1885
1886
1887
1888
1889
1890
1891
1892
1893
1894

1
( Q( Z , L) DL ( Z , L)dLdm
mT DT mT Z L.

(3.18b)(123) Similar to equivalent dose in an organ or tissue, HT, the value of dose equivalent inan organ or tissue is defined for organs and tissues in males and females by:
H T,MQ  QTM DTM and H T,F Q  QTF DTF .
(3.19)(124) In most cases the difference of QT for males and females is small and a tissue-meanquality factor, QT, may be used for both sexes.
(125) Based on the definition of effective dose, E, the effective dose equivalent, HE, canthen be calculated by applying the tissue weighting factors, wT, as given in ICRP Publication
103 (ICRP, 2007)

H E   wT H T, Q

(3.20)

T

1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913

where for HT,Q the mean value from doses for the male and female phantom is chosen. Notethat this quantity has already been defined by the Commission in Publication 26 (ICRP,
1977) but with different tissue weighting factors and replaced by effective dose in Publication
60 (ICRP, 1991).
(126) An application of effective dose equivalent, however, is not recommended for theassessment of doses of individual or small groups of astronauts when these should become abasis for risk estimates. The recommended wT values are single values for both sexes and also
based on data for persons of all ages including children. They are not appropriate for a
realistic risk assessment for male and female astronauts and hence risk estimates should bebased on either absorbed dose or dose equivalent data for the organs and tissues of males or
females respectively, and corresponding risk factors for these tissues for male and female
adults (see e.g. Table A.4.19 in Annex B of ICRP Publication 103 (ICRP, 2007)). If
necessary, also the age of the person considered may be taking into account. Even the quality
factor may differ depending if leukaemia or solid cancer induction or mortality is considered(see Fig. 3.14).
(127) If, nevertheless, a value of effective dose equivalent is needed for recording, HEshould be calculated by:

H EM   wT H T,MQ or

H EF   wT H T,F Q

T

1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927

(3.21)

T

depending on the sex of the astronaut.
3.3.2 Operational quantities(128) Radiation monitoring in a spacecraft and individual monitoring for each astronaut isa necessary measure for radiological protection in space and the assessment of mission dosesof astronauts.
(129) On Earth, area monitoring in terms of the quantity ambient dose equivalent, H*(10),provides in fields of penetrating radiation the information which exposure in terms ofeffective dose a person would receive when staying for a given time at the position of thearea monitor. In most external fields of strongly-penetrating radiation on Earth, only lowLET radiation, mostly x- and -radiation, partially also electrons, is present and in few cases
only neutrons are also important for radiological protection. As a consequence, most area
monitors used in radiological protection measure either photon or neutron doses and the total
59

DRAFT REPORT FOR CONSULTATION
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975

ambient dose equivalent is then achieved by adding both dose components. Concentrating on
photons, electrons and neutrons only has strongly influenced the idea of defining a special
measurable dose quantity in an appropriate simple phantom (the ICRU sphere) for area
monitoring and the assessment of effective dose.
(130) The consequence of the specific situation in space is that some concepts of thequantities used in radiological protection on Earth have to be revisited. For example, theoperational quantity for area monitoring of penetrating radiation which is based on the dose
equivalent at 10 mm depth of the ICRU sphere in aligned fields has been mainly designed on
the basis of photon and neutron data for control of effective dose and is limited in its
application to radiation with energies where secondary charged particle equilibrium can beachieved at about 10 mm depth in tissue. This is not the case for very high energy particles.
(131) In radiation fields in space with its large spectrum of different types of particles ofvery high energies the definition of H*(10) is inappropriate (ICRP, 2012) and it will bedifficult to define a dose quantity independent from the human body with the same properties
as ambient dose equivalent for photon and neutron radiation of conventional energy. In
addition, monitoring and assessment of doses in the human body during missions ofastronauts may not be restricted to effective dose equivalent and dose equivalent to the skin,
the lens of the eye and the extremities, but should include other organs and tissues of thebody, too. Hence no specific dose quantity for area monitoring in space has been defined up
to now. The monitors used serve mainly as instruments for recording the environmental
radiation outside or inside a spacecraft and for warning in cases of very intensive SPE´s.
They measure particle fluence, LET-distributions or absorbed doses in detector materials (seeChapter 4). These data are used as input or validation data for calculations of doses in thehuman body.
(132) In individual monitoring, the situation is similar to area monitoring and a dosemeter
calibrated in terms of Hp(10) in photon or neutron radiation fields on Earth and worn on the
body of an astronaut in space will not automatically provide an estimate of effective dose
equivalent in complex space radiation fields.
(133) A specific operational dose quantity for individual monitoring in space has not been
defined by ICRU or ICRP. Different quantities and procedures may be applied for anassessment of organ doses or effective dose equivalent (see Chapter 4). A combination of
measurements of absorbed dose and LET-distributions at the surface of the body may become
an appropriate way for individual dose assessment (see Sect. 4.3.3). Data from area
monitoring within the spacecraft combined with calculated dose conversion coefficients canalso be used to calculate organ dose equivalents or effective dose equivalents for personspresent in that radiation field (see Chapter 6). This, however, needs the knowledge of thefluence and energy distribution of all components of the radiation field which in addition mayvary with time. Furthermore application of methods of biological dosimetry may provide acomparative way of assessing mission doses of astronauts (see Sect. 4.3.4 and 6.4.2).
(134) Specific attention is needed for the measurement of doses from low-penetratingradiation, e.g. electrons or solar low-energy protons, which may contribute significantly todoses to the skin and the lens of the eye especially in situations when astronauts are working
outside the spacecraft or during large solar flare events.
3.3.3 Quantities for high doses(135) At high doses near to thresholds where deterministic effects (tissue reactions) may
occur, organ dose equivalent and effective dose equivalent should generally not be used for60

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an assessment of radiation risks. While HT,Q and HE may give an indication, if such dose
range is reached, risk estimates should be based on mean absorbed doses in organs or tissues,
maximum dose values in organs or tissues or on organ dose equivalent depending on theactual situation and the availability of risk factors for the different types of radiation anddoses involved. Generally tissue reactions occur above a threshold dose in the range of 0.5 - 2
Gy.
(136) The mean absorbed dose in an organ or tissue, DT, and the RBE weighted mean
absorbed dose, RBE·DT, when high-LET radiation is involved, is the appropriate quantity forassessing risks of deterministic effects at higher doses. The RBE-value to be chosen may
depend on the organ or tissue considered and the specific dose and dose rate as well on thetype and severity of the tissue reaction considered. In some cases of deterministic effects,
however, not only the mean dose in an organ or tissue but also a local dose in that tissue may
become important (e.g. local skin dose).
(137) The dose limits for tissue reaction are given in terms of the mean absorbed dose inan organ or tissue, DT, and this value weighted by an appropriate RBE should be applied. The
RBE values may be taken from ICRP Publication 58 (1989), where values of 6 (range 4 to 8)
for neutrons of energy 1 MeV to 5 MeV, of 3.5 (2 to 5) for neutrons of energy 5 MeV to 50
MeV, of 2.5 (1 to 4) for heavy ions, and of 1.5 for protons are recommended.
(138) Measurements of particle fluence, LET-distributions or absorbed doses can be
performed in any radiation field, even in strong radiation fields producing high doses, e. g.
during solar particle events, where non-stochastic tissue reactions cannot be completely
excluded. Measurements of Hp(d) which is defined by using the fixed Q(L) relationship may
also be performed in such intense radiation fields for the purpose of dose recording. For risk
assessment, however, it must be considered that the Q(L) function has been defined based on
RBEmax data at low doses and, therefore, its application in radiation is usually limited to the
low-dose range.

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2004
2005
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2007
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2009
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2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
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2050

4.

METHODS OF MEASUREMENT OF RADIATION FLUENCES
AND DOSES(139) Radiation transport calculations, measurements, and interpretation of data areessential components for operational radiation safety. The measurements include anassessment of the environment at the exterior surface of the spacecraft or habitat; assessmentof the interior environments in the spacecraft/habitat and EVA suit; the use of personal
dosemeters; and the determination of the transmission of radiation to internal organs or
tissues.
(140) Individual monitoring of occupationally exposed persons on Earth is mainly
performed to ensure that the exposure is below legal dose limits which are generally set tolimit exposure risks to an acceptable level. While the basic limits are given in terms ofeffective dose, it is generally accepted that at doses far below the limits the measured
personal dose equivalent appropriately assesses effective dose in routine radiologicalprotection applications (ICRP, 2007). The situation in space, however, is significantly
different. Doses to astronauts in space may be much higher than annual dose limits foroccupationally exposed persons on Earth, especially in long duration missions. It is,therefore, important to obtain more precise information about doses and exposure risks. For
planning purposes and for operational radiation safety programs, risk assessment is seen to be
as important as dose recording for astronauts in space. For any risk assessment, however, theknowledge of the radiation incident on the human body and/or the assessment of doses in thehuman body are basic preconditions.
(141) Calculations are essential to mission planning in that they provide pre-flightestimates of the doses that would be received by the astronauts during the different phases ofa proposed mission. They are also an important part of the dose assessment process fordetermining the doses received by the astronauts during the mission.
4.1

Measurement quantities(142) The objective of the adopted dose assessment approach in radiological protection is
generally to determine the specific protection quantities defined for the low-dose range forlimiting the probability of stochastic effects and for avoiding deterministic effects (tissue
reactions) in the human body. For applications on Earth these quantities are the equivalentdose in an organ or tissue, HT, and the effective dose, E (see Section 3.1). For the special
situation of astronauts in space, the quantities mean absorbed dose in an organ or tissue, DT,and dose equivalent in an organ or tissue, HT,Q, are proposed for use instead (see Section 3.3).
At higher doses when deterministic effects may occur, a differently weighted absorbed doseis required. In this case, a mean value of the relative biological effectiveness, RBE, needs tobe determined from the information on the radiation field components and the specific RBE
values of the different types of particles involved. There is an important role forbiodosimetry. Individual biomarker measurements on astronauts can give consolidation forother dosimetric approaches.
(143) The radiation environment external to a spacecraft in low Earth orbit consists ofelectrons, positrons, neutrons, protons and all stable atomic nuclei (up to charge Z = 92).
Particle energies range from a few eV for trapped electrons and from thermal neutrons to 1014
MeV for GCR (see Chapter 2). Most of the electrons will not penetrate the wall of thespacecraft, but could penetrate the space suits worn during extravehicular activity (EVA),
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2098

resulting in doses to the skin and lens of the eye. Nuclear interactions of neutrons, protons
and heavier nuclei with spacecraft, space suits, the Earth’s atmosphere and the human body
produce secondary radiation, which add to the radiation field. The techniques of radiation
monitoring vary according to particle type, energy, and the measurement location (inside oroutside the spacecraft, inside EVA suits). The radiation environment can be classified on thisbasis:•
Trapped electrons – outside spacecraft and inside EVA suit;•
Trapped protons (< 10 MeV) – do not penetrate spacecraft or EVA suit;•
Protons and light charged particles (> 10 MeV) – outside and inside spacecraft, andinside EVA suit;•
GCR and secondary photons – outside and inside spacecraft, and inside EVA suit;•
Secondary charged-particles – inside spacecraft and inside EVA suit;•
Neutrons - outside and inside spacecraft, and inside EVA suit.
(144) In addition to variations of the primary external radiation field the relative
contribution of each component (including the secondary radiation) to organ and tissue
absorbed doses and dose equivalents at each location will also vary according to additional
factors, including the mass distribution inside the spacecraft and the EVA suit construction.
(145) Mean absorbed doses and dose equivalent in organs and tissues of a human body are
generally not directly measurable. An approach to the estimation of these quantities is given
in Chapter 6. These include (1) calculations of particle type and energy and direction
distributions of fluence in radiation fields at the location of an astronaut plus the applicationof organ absorbed dose and dose equivalent conversion coefficients; (2) direct assessment oforgan absorbed doses and dose equivalents for an astronaut by radiation transport calculation
using energy and direction distributions of fluence from outside of the spacecraft, orotherwise, at the astronaut’s location; and (3) measurement of absorbed dose or dose
equivalent near or on the astronaut and the use of results from calculations applying
anthropomorphic phantoms.
(146) The main objectives of environmental measurements are the provision of radiation
field data of particle types, fluences and microdosimetric quantities, absorbed doses and dose
equivalents, using detectors in assemblies of various sizes, both integral and differential (withrespect to time, or LET, or energy, or direction, as appropriate) and, in some cases,
normalized to calculations of the radiation field components. For personal monitoring, thesame quantities might be determined, but more importantly data are required for thedetermination of absorbed dose and dose equivalent. Absorbed dose and dose equivalentvalues measured by personal dosemeters worn on the body can be applied as estimates of D
and H at a point in adjacent tissue, or can be used with prior data as estimates of absorbed
dose or dose equivalent to specific organs and tissues at larger depth. Environmental
monitoring can provide radiation field data as input for calculations which will yield
estimates of doses in the human body or may even be used to directly assess individual risks.
It may measure dose quantities such as absorbed dose, D, the distribution of D in L, D(L), or
dose equivalent, H. It can also provide measurements in support of in-flight dosemanagement, dose recording, and ALARA actions.
(147) The radiation detectors determine a particular measurement quantity. These include(1) particle type and energy and direction distributions of fluence; (2) dose deposition in thedetector material; and (3) other dosimetric quantities such as LET or lineal energy, y. In
addition there are calibration data on detector response and normalization of detector
response (for example normalized to equivalent water absorbed dose for a radiation type and63

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2100
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2110
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2114
2115
2116
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2119
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2121
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2124
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2132
2133
2134
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2138
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2142
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energy)(148) Several types of instrumentation are available including both active and passive
devices. Active instrumentation should have a time resolution sufficient to identify temporalvariations in the radiation field. Alarm or warning capabilities of instruments can be used tosupport in-flight implementation of dose management and ALARA actions. Passive detectors
provide an integration of the exposure information over long time intervals. They are usually
very robust, small in their dimensions and need no power supply. Some devices also allow
on-demand readout. For all instrumentation used for measurements in space the following
must be established: (1) full response characterization and calibration; (2) measurement
model; and (3) knowledge of uncertainties. Comparison of instrument responses is also
useful. Many details of instrumentation for dosimetry in space have been published in review
papers by Benton (2001), Badhwar (2002), and Caffrey and Hamby (2011). Further
information has been presented by the HAMLET collaboration (HAMLET, 2011).
4.2

Purpose of measurements(149) Measurements are performed for the purpose of determining individual exposures,monitoring changes of the radiation environment and performing ALARA. Instrumentation
positioned inside or outside of a spacecraft or habitat can provide essential data for thecharacterization of the primary fields impinging on the spacecraft, such as galactic radiation,
the trapped particle radiation field and the field caused by solar particle events. Such datafrom outside allow corrections to be made to the input data of transport codes to determine
the field inside the spacecraft or habitat and so can reduce dose assessment uncertainties. Ion
chambers or other active detectors with well-defined wall thickness can serve to monitor the
short-term variations in the electron environment for EVA.
(150) Selectively located active and passive instrumentation allows radiation monitoring
and further adjustments to the calculated internal environment. Particle spectrometers canprovide data for the evaluation of transmission factors and of response functions of
dosimetric devices and allow evaluation of calculated values and uncertainties of dosimetricquantities. Both active and passive devices are useful for determining absorbed dose,absorbed dose distribution over LET, absorbed dose distribution over lineal energy, andestimates of dose equivalent. Personal dosemeters worn by astronauts can determine some ofthese quantities at adjacent tissues.
(151) There are short-term and long-term variations depending on solar activity, which
modify the environmental radiation field (components, particle fluences, energies anddirection distributions), so that energy- and direction-sensitive instrumentation is mandatory.
In addition, active instrumentation allows the time-resolution of trapped, solar, and GCR
components.
4.3 Instrumentation for radiation spectrometry, area and personal monitoring
4.3.1 General(152) No single device can determine the required dose quantities for all components of
the radiation field. Since there are large variations in the relative contributions to total
absorbed dose and dose equivalent from the different particle types, it is not generally
possible to determine the absorbed dose or dose equivalent from just one component (or few
components) and apply a correction factor to determine the absorbed dose or dose equivalent64

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for the entire radiation field.
(153) The dosimetry may be simplified by considering separately the radiation in terms of
its energy deposition properties characterized by LET (or lineal energy). These include both
low-LET charged particles (those of LET less than 10 keV/µm) and high-LET charged
particles (those of LET equal to or greater than 10 keV/µm). High-LET particles may beseparated into the high-energy heavy ions (Z >2) and their fragments, and the mainly highLET particles produced by the strong-force interactions of neutrons and high-energy protons.
Often separate dose measurements are performed for these categories, preferably minimizing
any overlap of response to avoid “double counting”. The choice of measurement devices isdictated by radiation response characteristics (dependence on particle type and energy and on
the quantity to be determined), operational characteristics (direct determination of dosequantities, input to model calculations, desired accuracy, dose management and ALARA
support), as well as practical issues such as reliability, robustness and availability. The
addition of devices measuring y and L distributions of energy deposition in tissue from allparticles has substantially improved the situation of dosimetry in space.
(154) Another important consideration is the time required for analysis of the measured
data compared with the duration of the mission. It might be desirable for long duration
missions that there are read-out facilities for passive devices on board.
(155) Additional passive personal dosemeters may be needed on the astronauts during
EVA missions to take account of the spatial variations in the degree of shielding provided by
the spacesuit and the spacecraft.
(156) The development of a set of coefficients that directly relate dose equivalent obtainedwith TLDs and NTDs at the surface of a body to mean organ absorbed dose or dose
equivalent for the space radiation environment is desirable in principle. It is, however, a very
difficult task due to the complexity of the radiation field in space. While it might be possible
for the GCR component, it seems to be impossible for trapped radiation owing to its strong
variation with time and location.
(157) Neutrons are indirectly ionising particles. They are generated by interactions of
GCR and higher-energy protons with the atmosphere of Earth, or other body, the spacecraftor habitat, or within fellow astronauts. The energy distribution of those neutrons has several
maxima due to reactions producing neutrons from the incident GCR nuclei or the target
atoms in spacecraft materials or tissue. The lowest energy maximum occurs as about 1 MeV
from neutrons produced from the nuclear evaporation process from target atoms ininteraction with GCR. A second broader maximum occurs at about 100 MeV from knockout
and cascade reactions leading to fast neutrons from emitted from target nuclei. At higher
energies, there is an even broader maximum near about 1000 MeV due to neutrons produced
from the GCR nuclei by either evaporation or knockout and cascade reactions. Various
methods are applied for neutron monitoring in space (see e.g. Benton et al., 2001). To detectabsorbed dose to tissue and dose equivalent from the high-LET secondary particles fromneutrons, and for similar particles produced by strong-force interactions of higher energy
protons, it is necessary to use detector materials and local shielding that closely matches
tissue elemental composition.
4.3.2 Active devices(158) Active devices record and display data in real time, or near-real time. This enables
measurements of fluence or dose rates as well as time integrated values. Most active
instruments can be turned on or off so as to operate in specific circumstances such as EVA
65

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and during an SPE. Active detectors require electrical power that can be provided throughconnections with power supplies in the spacecraft or through batteries. During recent years a
broad range of different types of active instruments has been used for radiation measurements
on board of the ISS either for scientific investigations (see Table 4.1) or for operational area
monitoring (see Table 4.2). In the following some types of instruments are described.

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2203

Table 4.1. Active radiation detectors applied on board the ISS for scientific applications during
recent years, some of them in combination with the MATROSHKA phantom (Dettmann et al., 2007).
Instrument

Measured parameters

DOSTEL – Silicon
Telescope
SSD – Silicon
Scintillator Device(Reitz et al.,
2009)

Christian Albrechts University Kiel, Absorbed dose, neutron
German Aerospace Center, Cologne dose, organ dose

LIULIN – Silicon
Detectors(Dachev etal., 2006)

Solar Terrestrial Influences
Laboratory, Bulgaria

ALTCRISS –Silicon strip detector(Casolini etal., 2007)
INFN and University of Rome Tor(Fuglesang, Vergata, Rome, Italy
2007; Narici
et al., 2004)(Koshiishi et Japan Aerospace Explorational., 2007)
Agency, JAXA, JapanALTEA –
Silicon strip detector
BBND – Bonner Ball
Neutron Detector
Table 4.2.

International collaboration

Various parameters

Christian Albrechts University Kiel, LET distrib., absorbed
German Aerospace Center, Cologne dose, dose equivalent

Absorbed dose, dose
rate
Particle energy distrib.
up to Iron nuclei,
LET distribution, dose
equivalent
Neutron energy distrib.
and neutron dose

Active and semi-active radiation detectors used on board the ISS for area monitoring.

Instrument
Tissue equivalent
proportionalcounter (TEPC)
Charged particle
detector system(IV-CPDS)
Charged particle
detector system(EV-CPDS)
Ionisation
Chamber (R-16)
Silicon detector
units (DB8)
TL – system(PILLE)

2206
2207
2208
2209
2210
2211
2212
2213

Heritage(Reitz et al.,
2005)
(Reitz et al.,2009)

DOSMAP

2204
2205

Ref.

Ref.

Heritage(Badhwar etal., 1994)(Lee et al.,2007)

(Benghin etal., 2008)(Apáthy et al.,
2002; 2007)

Measured parameters
LET distribution, absorbed
dose, dose equivalent

NASA Johnson Space
Center, Houston

LET distribution, particle
energy distribution, Nuclear
abundances up to Oxygen

Moscow State University,
Moscow

Absorbed dose, dose rate

Space Research Institute,
Bulgaria

Absorbed dose, dose rate

KFKI, Hungary

Absorbed dose, dose rate

Tissue equivalent proportional counters(159) A tissue equivalent proportional counter (TEPC) is a low-pressure proportionalcounter with a wall of tissue-equivalent material especially designed for use in
microdosimetry and radiological protection. The pressure of the gas in the detector is chosen
to simulate a volume of tissue comparable to the dimensions of the nuclei of a mammaliancell. The charge produced by an ionising particle traversing the chamber volume is collected67

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and, by calibration of the detector, the electrical signal can be related to the energy loss of thecrossing particle in that simulated tissue volume. Data are recorded on an event-by-event
basis such that one can obtain a distribution of energy deposition events in a small element oftissue with a known covering material in terms of lineal energy, y, which can be correlatedwith LET, and therefore characterizes the ionisation density along tracks of particles andradiation quality. The lineal energy, y, is defined by the quotient  l , where  is the energy

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transferred to the chamber gas by ionisation by a crossing particle and l the mean path
length of the charged particles in the chamber volume. Consideration should be given to
factors which influence performance, such as wall effects.
(160) The response to photons and neutrons depends on the probability of the productionof secondary charged particles in the wall passing the detector volume - and hence on thewall material. Mostly materials that are tissue-equivalent with respect to neutrons are chosen,
for example A-150 plastic. For incident charged particles, each particle crossing the chamber
volume produces a signal. Depending on the shape of the volume, even for incident
monoenergetic charged particles a broad y-distribution is obtained. The y-distribution isfurther modified by straggling effects and secondary charged particles produced in thechamber wall (see Fig. 4.1).

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2239
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2246

Fig. 4.1. Frequency distribution, f(y), of lineal energy in a TEPC for a uniform fluence of 56Fe ions.
Curves 1 and 2 are calculated by taking the chord length in a sphere (curve 1) and a cylinder (curve 2)
times the LET of the Fe-ion. Data of Curve 3 are from measurements with a spherical detector andCurve 4 is the results of a calculation using restricted LET, L, and considering straggling (NCRP,
2002).

(161) The term y·f(y) as a function of y approximates the dose distribution in terms of LET
and can be used to determine a mean quality factor for the absorbed dose to the detector
configuration (Doke et al., 2001). When the data are integrated over the distribution of y orL, the TEPC can generate absorbed dose and absorbed dose rate. Data from a TEPC can bedisplayed continuously or stored for later transmission to mission control. Special TEPC
systems have been designed for use in spacecraft (see e.g. Caffrey et al., 2011).
Semiconductor devices
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(162) Semiconductor devices for the detection of charged particles are thin diodes, mostly
Si-diodes (thickness of about 50 to 5000 µm), that record the energy deposited by a charged
particle in the sensitive volume of the detector. For particles with normal incidence and fully
traversing the sensitive detector volume, the ratio of the deposited energy to the thickness ofthe detector yields the approximate LET for the incident particle in that material. If charged
particles from various directions pass the detector, a mean path length in the sensitive
detector volume need to be determined for assessing an LET-distribution. Thus, a single
detector can approximately provide an estimate of the charged particle fluence distribution in
linear energy transfer and time. This distribution can be integrated to yield dose and dose rate
for protons and heavier charged particles in the detector material, and by the use of
conversion coefficients, determine dose to tissue. Often some detectors are used as atelescope which restricts the response to a smaller solid angle.
(163) Several multi-array solid-state detectors are combined to form a particle telescopethat measures both energy deposition and flight direction. When these data are combined, thedetector yields a more accurate estimate of LET in the detector material, and thus the
distribution of fluence in LET, direction, and time. Using appropriate conversion coefficients,
the data can also be used to obtain D(L) distributions and Q-values for heavy charged
particles, but with the restriction that the incident particles originate from a fixed direction
depending on the orientation of the detector. Because of size limitations, this type of detector
is only sensitive over a restricted solid angle.
(164) The energy lost in solid-state detectors of a telescope can also be used to identify theparticle charge as well as the incident energy to ultimately obtain the distribution of fluence
in energy, particle charge number and time. Several of these detectors can be combined topoint in different directions to provide a more complete description of the radiation field
either outside or inside a spacecraft.

(a)

(b)

Fig. 4.2. Charged particle spectrometer DOSTEL designed for space applications (Posner et al.,2005). Schematic view (a) and realized detector (b) (Beaujean et al., 2002).

Direct ion storage devices(165) This device combines an ionisation chamber with a semiconductor device.
Specifically, the direct ion storage dosemeter, DIS, is based on coupling a gas-filled ion
chamber with a semiconductor non-volatile memory cell where the charges produced in thechamber volume are stored. These are compact integrating devices that can be read out
periodically without deleting the information and are used to estimate accumulated doses

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over periods of several hours to at least one year. The response of the DIS to charged
particles incident on the detector and passing the chamber volume is approximately equal tothe energy deposited, while the response to photons and neutrons incident on the DIS andproducing secondary charged particles in the detector depends on the material and thicknessof the chamber wall. The response to low-energy charged particles incident on the DIS
depends also on the chamber wall thickness due to their energy loss in the wall.

Efficiency relative to absorbed dose in water

Relative response, 1/Quality factor

1.6
1.4
1.2
1.0
0.8

0.6
0.4

0.2
0.0
238Pu-Be

2292
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2312
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2317
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2319
2320
2321

CERF

in beamin beamin beam(centre)(edge)(corner)

LET(H2O) / keV mm -1

Fig. 4.3. Relative response of the DIS-1 dosemeter.
(a) Dosemeter reading in terms of personal dose equivalent, Hp(DIS), normalised to absorbed dose in
10 mm depth of tissue, D(10), (triangles), and ambient dose equivalent, H*(10) (squares). The inverseof the quality factor, 1/Q, is also indicated (diamonds) (Otto, 2010).
(b) Efficiencies of DIS-1 relative to absorbed dose in water as a function of LET(H2O). Each pointfor 60Co- radiation, carbon and iron ions represents an average value from six samples (1 s.d.). Twoof the samples were irradiated with each of three doses (10 mGy, 25 mGy, and 50 mGy in water).
Points for 137Cs- radiation, helium ions and argon ions represent two samples irradiated with a doseof 10 mGy. (Yasuda, 2001).

Bonner sphere spectrometer(166) In principle, a Bonner sphere spectrometer consisting of a set of Bonner spheres ofdifferent size is well suited for measuring neutron fluence and spectral distributions ofneutrons. On ground, neutrons over a wide energy range are often monitored by suchmoderator-based survey instruments whose responses have also been extended to higher
energies by introducing a layer of heavy metal in their moderator (see e.g. Wiegel et al.,2000). However, those instruments are not suitable for use in spacecraft because of theirheavy weight as well as their high sensitivity to HZE particles. A Bonner Ball Neutron
Detector (BBND) was used on Space Shuttle flight (Matsumoto et al., 2001) and on ISS(Koshiishi et al., 2007) for measuring the fluence of neutrons with energies below about 15
MeV. However, also high-energy neutrons are present in spacecraft (see par. 158). Thus,
development of a new instrument having a light weight and less sensitivity to HZE particles
is necessary for precisely monitoring neutron fluence or doses in spacecraft.
Electron detectors(167) Active electron detectors need to be specially configured to measure low-LET
radiations, in particular, electrons below about 1 MeV. Electrons of these energies arenormally not an issue inside the spacecraft but could be of concern during EVA, sinceelectrons above a few hundred keV can penetrate the spacesuits. Since the trapped electron
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fluence rate can change by many orders of magnitude during and following a large magnetic
storm, due to short-term perturbations of the geomagnetic field, it is recommended that an
active detector sensitive to electrons be installed outside the spacecraft to serve as a monitor
for fluctuations in the electron component of the space radiation environment to enable dosemanagement during EVAs. Such a monitor could be a simple ionisation chamber or solidstate detector with a wall thickness sufficient to strongly attenuate very low energy electrons
but thin enough to record electrons that could penetrate a spacesuit (Evans et al., 2008).
Active personal dosemeters(168) Active personal dosemeters (APD) can give an instant indication of bothaccumulated dose and dose rate. Preset visual and audible alarms are also provided, so thatthese devices can be used simultaneously as an integrating dosemeter and as an alarm
dosemeter. APD can be used as supplementary dosemeters to a passive dosemeter used forroutine dosimetry. It is clear that for low-LET radiation the energy and directional response
characteristics of APD are, in most cases, as good as passive dosemeters, able to measuredoses in continuous radiation fields with acceptable accuracy.
(169) An ideal personal dosemeter would be active, store integrated dose data and dose
rate time profiles, and respond to all field components allowing a sufficiently precise
determination of absorbed dose rate and dose equivalent rate to adjacent tissues. Most
available electronic personal dosemeters have been designed to measure absorbed dose totissue under a defined covering layer from photon and beta radiation and their high-LET
response characteristics are not well determined. Such dosemeters might be considered forthe measurement of the low-LET component of the fields in spacecraft/habitat. However,even if used only to determine the low-LET component, a full characterization of theircharged-particle and neutron response is necessary. Pixel-based detectors can be used as
personal dosemeters. They can provide energy deposit distributions, energy and charge for allparticles. They are based on a read out chip that embeds the electronics for each pixel within
the pixel´s footprint. Careful calibration is necessary as for other devices.
(170) If active personal dosemeters are not used, then it may be necessary to develop onboard readout capabilities for passive dosemeters, especially on long-duration missions inspace. Although on-board readout of nuclear etched track detectors is not feasible, on-board
systems for readout of TL- and OSL-dosemeters already exist.
4.3.3 Passive devices(171) Passive devices can be used for both area monitoring and personal monitoring. No
single passive device is capable of dose measurement across the full energy and direction
distribution of particles available in space. The instrumentation and detectors should bedesigned to have optimum performance in the types of particles noted above, namely: lowLET charged particles (i.e. L < 10 keV µm-1), including such particle produced by nonionising particles incident on the instrumentation; high-LET charged particles from neutronsand protons that undergo strong-force interactions; and high-LET heavy charged particles(HZE). While thermoluminescence detectors (TLD) radiophotoluminescence glasses (RPL),
and optically stimulated luminescence dosemeters (OSLD) are used mostly for photon andelectron dosimetry, as well as for neutron dosimetry, plastic nuclear etched track detectors(PNTD) are well suited for measurements in neutron and heavy charged particle fields. In
space applications, measurement systems combining both detector types are often used inpersonal dosimetry.
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Luminescence detectors(172) Passive dosemeters currently in use are mostly thermoluminescence detectors(TLD). TLDs are small sintered chips or pellets of crystals which show luminescence after
exposure to ionising radiation. By fast controlled heating of the crystal, the stored energy isreleased as light emitted. The function between the actual temperature and the intensity of theemitted light (the glow curve) shows various peaks, the heights of which are proportional toabsorbed dose. Various crystal materials doped with different elements are in use for personal
dosimetry.
(173) An alternative to TLD is the use of radiophotoluminescense glasses (RPL). Small
glass elements respond as do TLDs to incident ionising radiation, storing energy inmetastable electronic levels. The energy is released as light when the glass is exposed to ultra
violet laser illumination.
(174) Optically stimulated luminescence dosemeters (OSLD) have also be proposed. In
OSLD, the stored energy is released by optical laser stimulation. TLDs, RPL glasses, OSLD
material, or similar types of dosemeters, will have to be fully characterized for the specificspace environment.
(175) There might be a need for some passive elements to be read out frequently on board,and others that are read only on return to Earth. The mode of readout of the luminescence
dosemeters should be carefully considered.
(176) TLDs, RPL glasses, and OSLDs measure absorbed dose in their material and aremostly calibrated in terms of absorbed dose in tissue or water in 137Cs or 60Co gamma
radiation reference fields. The detector response, relative to the response to the reference
radiation depends on the ionisation density around the track of a traversing particle. While for
L < 10 keV/μm there is mostly only a small L-dependence of the response, TLDs, RPL
glasses, and OLSDs show a strong LET-dependence above about 10 keV/μm, generally withdecreasing response with increasing LET (see Fig. 4.4). This needs to be well known for
dosimetry in space radiation fields. Fig 4.5 shows the relative variation of the response ofsome TLDs to cosmic radiation and ions with different LET-values in the detectors.
1.4

Relative response

1.2
1.0
0.8

0.4
0.2
0.0
10-1

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H
He
 C

O
 Ne
 Ar
 Fe
 Nb


0.6



100

101

102

103

LET in H2O / keVmm-1

Fig. 4.4. Relative Fig.
response
of TLDs for various charged particles. The relative response (relative to
4.4
60
Co- rays) of peak 5 from TLD-600 and TLD-700 versus mean LET (in water) in the detector isshown (Benton et al., 2000; Berger et al., 2006).

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Relative response

2403

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LET / keV mm-1
4.5
Fig. 4.5. Relative Fig.
responseof various TLDs (normalized to the mean value) to cosmic radiation andion beams with different LET values in the detector; current results of the intercomparison of personal
dosemeters (HAMLET) (Bilski et al, 2011).

Nuclear track detectors(177) To detect the high-LET component of the radiation field, plastic nuclear etched track
detectors (PNTD) and nuclear emulsions can be employed. Damage to the material is causedby the passage of a charged particle, and these particle tracks can be viewed microscopically,
either before or after being realized by suitable chemical treatment. Etched track detectors are
generally insensitive for radiation with an LET in water below about 10 keV µm-1 (dependingon material) and may be employed in a method that provides D, D(L), or D averaged overcertain ranges of L, and H. With suitable detector sets, etched track detectors and nuclear
emulsions can determine the charged particle type and its direction in the detection medium,and can allow an analysis of the radiation field at the position of the detector. The analysis of
the response of polyallyldiglycolcarbonate (PADC), commonly named CR-39, in terms of thedependence on LET allows the determination of absorbed dose and dose equivalent to a small
element of tissue from all charged particles above about 10ֺkeVֺµm-1 (Zhou et.al., 2006). The
detectors can separate the heavy charged particle and neutron contributions by looking at theparticle ranges. A further separation procedure to detect the neutron dose component can bemade using thin detectors and coincidence techniques or by using of a thin PADC detector
and a combination of electrochemical and chemical etching. Stacks of PADC detectors canbe used for spectrometry of HZE particles (see e.g. Gunther et al., 2002)

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109

Relative response8



USF3 Data (C-, Ca- and Fe-ions)
USF4 Data (C-ions)

7
6
5

4
3
2

1

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1

10

100

LET200,CR 39

1000/ keV mm-1

Fig. 4.6. Relative response of PADC detectors (CR-39) as a function of restricted LET, L200
Fig. 4.6(O´Sullivan et al., 1999; Zhou et al., 2008).

Superheated emulsions(178) Superheated emulsion detectors, sometimes referred to as superheated drop or
bubble detectors, are small droplets of a liquid above its normal boiling point suspended in a
viscoelastic medium. The droplets remain in the liquid phase until a charged particle interacts
inside or near the surface of the droplet. This transfers energy to the droplet and may cause
local evaporation. If sufficient energy has been transferred and a critical radius is exceeded,
all the liquid in the droplet will be vaporized and the bubble becomes visible. Superheatedemulsion detectors respond to neutrons and to heavy-charged particles. A clear calibration
procedure is required. Recent data on bubble detector responses are presented by Lewis et al.
(Lewis et al, 2012).

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Combined detector systems(179) A combination of one detector for the measurement of the low-LET component and
one for the high-LET component can allow the determination of dose equivalent in thecomplex radiation field in space. For passive dosimetry, with a package of TLD (or OSLD)
and PNTD, the dose equivalent in adjacent tissue near the surface of the body is determined
by:

2448

H  DTLD 

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

TLD
L 10keV/mm( L) DTLD ( L)dL DETDL 10keV/mm( L)Q( L)dL ETDL 10 keV/mm( L) DETD ( L)dL

(4.1)

where DTLD is the total absorbed dose recorded by the TLD (equivalent also for OSLD).
DPNTD(L) is the absorbed dose distribution in LET determined by the etched track detector in
the high-LET range (L > 10 keV μm-1) and for which Q is dependent upon L. The correction
terms consider the non-zero response of the TLD. ηTLD(L) is the relative dose response in theregion L > 10keV/μm and ηETD(L) that of the PNTD, respectively, in the region
L<10keV/μm, so that intermediate LET components are not considered twice. It is
recognized that this requires the verification of the LET-dependence of both the low-LET andhigh-LET detector system, and the elimination of parts from overlapping of responses.

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

TLD
ideal

actual1

LET

0

10 keV/mm

Fig. 4.7.

idealactual

1

0

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ETD



LET
10 keV/mm

Schematic relative dose responses of a TLD and a PNTD.

(180) An alternative method is to obtain data on the y or L distribution of energy
deposition from a TEPC or a particle spectrometer used as a passive area dosemeter, and to
apply this for correcting a measurement with a low-LET detector to obtain the full dose
equivalent at the dosemeter’s location. For such a correction the efficiency function, ε(L), of
the low-y or low-LET detector needs to be known, and an effective efficiency to be
determined.
4.4

Biomarkers of exposure(181) Biomarkers of health effects can be divided into 3 categories (Brooks, 1999):
biodosimetry which is a measure of exposure, biomarkers of risk, and biomarkers of thepresence of disease. The term biodosimetry in this context refers to a biological measurement
to assess a biologically based dose equivalent. Because of the complex nature of the spaceenvironment, including nuclear and atomic processes occurring within tissues, and the large
uncertainties in conversion of doses to risk, biodosimetry is routinely performed on the small
population of astronauts involved in International Space Station (ISS) missions, and would
likely be used in future space missions. There are also limitations in the size of devices thatcan be worn and practical obstacles to wearing a physical dosemeter at all times in space,which make biodosimetry an attractive supplement to physical dosimetry. To be useful as abiodosimetry method, the radiation quality dependence of the response of the assays should
be similar to the Q(L) relation from Eq. (3.10). Biodosimetry assays would likely be carriedout on lymphocytes from a routine blood sample (see e.g. IAEA, 2011). Biomarker assays
may require samples from other tissues including skin, swabs from the oral cavity to collectcells, urine or bone marrow. There are several biodosimetric methods that can be used forspace travel which are summarized next.
Micronuclei(182) Micronuclei result from loss of whole chromosomes or acentric chromosome
fragments from daughter nuclei following cell division. They appear as small, membranebounded inclusions in the cytoplasm. Their assessment is relatively easy and rapid and byincluding cytochalasin B in the cell cultures analysis of cells is restricted to those in their 2nd
post-exposure cycle. This has greatly increased the sensitivity of the assay. If individual preexposure levels of micronucleus frequency are available, absorbed doses as low as 50 mGy
can be detected; without knowledge of the background frequency the detection level is75

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estimated to be 100 mGy. A modification of the assay uses a fluorescent pan-centromere
probe to distinguish two types of micronuclei - those derived from either whole chromosomes
or from chromosome fragments. By restricting analysis to the fragment type much of the
background noise in the assay can be reduced (Vral et al., 1997).
(183) The frequency of micronuclei has been used for estimating exposures for a numberof radiation accidents with reasonable agreement with physical dose estimates. The
drawbacks are that few studies have been performed with high-LET exposures, and the assay
is not reliable for partial body exposures. Micronuclei are unstable structures meaning that
their frequency reduces with time due to the turnover of lymphocytes. This makes the assay
unsuitable as a biodosimeter in astronauts exposed to space radiations over prolonged
missions.
Acentric fragments in prematurely condensed chromosomes (PCC)(184) Interphase chromosomes can be prematurely condensed to be observablemicroscopically either by fusion with mitotic cells or by treatment with a phosphataseinhibitor (calyculin A) (Blakely et al., 2003). Structural and numerical chromosomal
alterations can be observed as an increase (or decrease) in centric chromosome number orfrom the presence of acentric fragments. The method has been used in a laboratory setting toassess exposure to x-rays and gamma radiation. The advantages are that non-dividing cells
can be used for assay and the analysis is quite straightforward. The current drawback is thatthe assay has had no application as a true biodosimeter, and issues such as responsiveness topartial body exposures or chronic exposures have not been addressed. Further investigation
appears warranted for assessing the value of PCC as a biodosimeter in the space environment.
(185) The fact that this PCC method has not been used in biodosimetry means that a lower
detection level has not been established. A reasonable assumption is that it will be no moresensitive than other cytogenetic methods, given similar cell numbers analyzed. The
advantage is a greater ease in obtaining large numbers of cells for analysis. As withmicronuclei, this signal also is unstable with time due to the replacement of lymphocytes
from the stem cell pool.
Chromosomal aberrations(186) The method that has been most extensively used in biodosimetry is that of theanalysis of structural chromosome aberrations. The incorporation of fluorescence in situ
hybridization (FISH) techniques (Cornforth, 2001; Edwards, 2005) has enabled theassessment of symmetrical (transmissible) translocations. Unlike the assays described above,these are stable aberrations that pass successfully through cell division and are more suited toprolonged space missions. This allows for reliable dose estimation at long times after
exposure. Chromosome aberration dosimetry has been successfully applied to radiation
accident victims, A-bomb survivors and a wide range of occupationally and medically
exposed persons including astronauts (George, et al., 2001; Cucinotta et al., 2008). These
scenarios include chronic exposures and partial body exposures for which specific methods
have been developed to aid in exposure estimation. The distribution of aberrations amongcells is useful in this regard. Even with this strong record of success, the application of themethod for dosimetry in astronauts in space has some drawbacks as evidenced by publishedstudies (reviewed in Testard and Sabatier, 1999; and by Obe et al., 1999). One problem is theinter-individual variation in response which, however, can be overcome by individual
calibration and determination of background in advance. The response is generally low due tothe nature of the exposures by which only a small number of cells will actually be traversed.
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This is especially the case for heavy charged particles. On the other hand, the effective area(or volume) of the blood system which is distributed over the whole body, is much larger
than that of a passive dosemeter – biodosimetry sees the rare events better than a small
physical dosemeter.
(187) Additional laboratory investigation is required in order to consider using cytogenetic
analysis as a reliable dosemeter for space missions. Biodosimetry assays take skilled
technicians to implement. The level of skill and time, however, to analyze data is no moredemanding than physical dosimetry and the costs of biodosimetry are lower than physicaldosimetry if the launch mass and crew time involved for physical dosimetry is considered.
(188) The detection of low doses using chromosomal aberrations is dependent upon thenumber of cells analyzed and whether an individual calibration curve is made prior to the
exposure of interest. This point is addressed by Bauchinger (1995) who estimates that for
5,000 cells analyzed (using a generalized background frequency for dicentrics) a significant
increase in dicentrics should be observed at about 100 mGy for a group of individuals.
Twenty thousand cells would need to be analyzed to detect 50 mGy. Knowledge of the preexposure dicentric frequency can lower this detection level without increasing the number ofcells analyzed.
(189) The study by Tucker et al. (1997) reports a lower detection level of about 500 mSv
of effective dose for occupationally exposed individuals using FISH analysis of stable
aberrations. The exposure was chronic in this case; a situation for which this type oftranslocation analysis is particularly applicable. Again, the sensitivity of the assay would be
increased by having available the pre-exposure aberrations frequency. It might be further
increased if the dose response to a reference radiation is determined using a blood sample
obtained prior to space missions (George, et al. 2001). The number of painted chromosomes
used also impacts the sensitivity of the assay. The older studies painted only one or two
chromosomes. Newer studies involved a larger number of chromosome paints or painting theentire genome which increases the sensitivity. Tucker has recently reviewed the low-dosesensitivity of the FISH translocations assay (Tucker, 2008).
Other biomarker methods(190) Several other assays as biomarker approaches have been proposed or recently
developed. These include complementary DNA (cDNA) arrays to measure gene expression(Mezentsev et al., 2011), prolonged life span of erythrocytes bearing transferring receptors
on their membrane (Gong et al., 1999), gene mutation assays, and electron paramagnetic
resonance (EPR) spectroscopy. A review on EPR dosimetry with tooth enamel is given by
Fattibene and Callens (Fattibene et al., 2010). For these methods to be applied to spacebiodosimetry, the dose, radiation quality and duration of the signal over many months willneed to be understood. A more recent assay is the measurement of telomere length.
Telomeres are the short repetitive DNA regions that cap the end of chromosomes protecting
them from deterioration. Reduction in the average length of the telomere has been associatedwith several late effects including cancer, neurological disorders, and aging (Schoeftner et al.,2009). Measurement techniques include southern blot, Q-FISH (Williams et al., 2011), andflow cytometry. These latter two assays allow rapid analysis of many cells. However, theradiation quality and dose response of the assay to protons and heavy ions irradiation will
have to be studied further before it can be considered for a deployable biodosimeter for space
missions.
4.5

Instrument characterization and calibration
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(191) For instrument characterization and calibration in a laboratory, it is necessary toclearly specify the relevant calibration conditions, including the characteristics of thereference radiation source, the irradiation facility, and the conversion coefficients used.
Periodic, accurate calibrations are essential, as are meaningful instrument responsecomparisons. Calibration (ISO, 2007; JCGM, 2008a) covers a number of the procedures
included in a type test. In the first step, a series of calibration factors (or calibration
coefficients, see below) or responses may be determined for a set of reference conditions,
usually a set of radiation energies and angles, to establish a matrix of calibration
factors/coefficients or responses, or a calibration/response function. The second step, whenused, applies these data to obtain the value of the desired quantity from the instrument
indication.
(192) All instrumentation should be fully tested prior to use. This procedure is especially
important for applications in space where an exchange of instruments during a mission isoften not possible. Failure of any part of the test should be clearly detailed and reasons for the
failure considered. Fully tested means the determination of the instrument performance
characteristics, including detection limit; tests of influence quantities, including other particle
field components; and tests of the reliability of the complete system, including system
software.
(193) For a fully tested instrument, a reference calibration (determination of a single
calibration factor or calibration coefficient for one set of reference conditions) is sufficient toensure a traceable absolute dose measurement. The reference calibration of the instrument
should be repeated at regular intervals. This may not be possible in space applications, butthen there should be periodic checks on the performance which may be carried out using nonreference fields and a fixed procedure. In addition to the type test, some instrument shouldhave a traceable individual normalization/calibration factor. For reusable dosemeters, thisfactor should be checked periodically and adjusted if necessary.
(194) The response characteristics of all the types of devices should be determined by a
combination of calculation and measurements. By Monte Carlo or other simulations the
response of an instrument is determined in terms of particle fluence, and its energy
distribution. The energy dependence of the response should be simulated for the particle
types and range of energies relevant to the radiation fields in space, plus the angle
dependence of response of the instrument, if any. The simulated instrument response must be
benchmarked in reference radiation fields. For the simulation of the response characteristics
of personal dosemeters, some irradiations should be performed with the dosemeter positioned
on either an anthropomorphic phantom or a surrogate.
(195) Where an instrument consists of more than one detector or more than one signal
channel, the result of any algorithm to calculate the measured value is to be treated as the
instrument indication in all determinations of calibration coefficient or factor or response.
(196) Experimental response data for the active and passive devices used should bedetermined for the following energy ranges as appropriate: protons from below 10 MeV to 1
GeV; helium from 10 MeV/u to 1 GeV/u; high-Z, high-energy ions (e.g. C, Si, Fe) from 50
MeV/u to 1 GeV/u; electrons from 0.5 MeV to 10MeV; and neutrons from about 1MeV to400MeV, monoenergetic or quasi-monoenergetic; plus response data for fields which
replicate the field produced by the interactions of GCR with shielding material. All theradiation fields used must be well characterized and traceable to national standards (NMI) or
related to NMIs via a traceability network (for example, quasi-monoenergetic neutron fields)
or as part of an international comparison programme (for example, ICCHIBAN (Uchihori et78

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al., 2002; Yasuda et al., 2006)).
(197) There are a number of ISO standards for photon, beta and neutron radiation,
covering radiation fields for most radiation protection situations on Earth. The situation forspace applications is more complex. Well specified mixed radiation reference fields with very
high energy particles and a large component of heavy ions do not exist on Earth. There areradiation fields available at very high energy accelerators (for example EG at GSI in
Germany; HIMAC, TIARA, CYRIC, and RCNP in Japan: NASA Space Radiation Lab at
BNL in the USA; TSL in Sweden; NPI in the Czech Republic; iThemba in South Africa;
NFS in France, CERN in Switzerland) which include a broad range of secondary particles
produced in the shielding surrounding a target. Such radiation fields replicate components of
the radiation fields in space and have been used for testing and intercomparison
measurements of various detector systems (Mitaroff et al., 2002). The precise specification ofthese radiation fields, however, can be a problem. Calculations are needed for the beam
particle and secondary particles, fluence rate and its energy distribution, plus any scatteredcomponents. The specific detector response to heavy ions can also be determined using
beams from heavy ion accelerators where the fluence rate of the heavy ion considered is well
specified.
(198) Determination of the dosimetric characteristics of the instrument (device or
combination of devices) and its reference calibration are closely interlinked. The result of a
response characterization is the detailed description of the dosimetric properties of a given
instrument. This includes the dependence of the response on particle type, energy, angle ofradiation incidence, and on various influence quantities. A reference calibration without aprior dosimetric characterization can be misleading, as the calibration can be misinterpreted
as applying to the radiation field in space without correction. An instrument dedicated to a
specific type of radiation (e.g. to neutrons) can have a response also for other particle types.
This needs also to be taken into account by calibrations.
(199) In modern instruments, the software has become of increasing importance for thegeneration of the measured value. Therefore, the final version of the software should beavailable at the beginning of the type test, as a great part of the software test is indirectly
covered by the metrological test. The manufacturer should be aware of the fact that any
change of the software may invalidate the type test. Dosimetry system software should be
guided by the WELMEC software guide 7.2 (WELMEC, 2008).
4.6

Accuracy and uncertainties for measurements in spacecraft(200) Astronauts are exposed to complex, multi-component fields that are difficult todetermine routinely. Radiation quality-weighted organ absorbed doses can be significant, anda main objective is that the uncertainties in the fluence rate and its energy distribution and in
the assessments of detector absorbed dose and radiation quality should be minimized.
Nevertheless, one of the objectives should be to meet the general requirement that the total
relative combined standard uncertainty of detector absorbed dose or dose equivalent should
be minimized. The total relative uncertainty in a subsequent estimate of organ dose or dose
equivalent will be greater.
(201) The uncertainty in measurement assesses the measurement accuracy or metrologicalquality of measurements or fitness for purpose of a measured quantity value. Measurement
accuracy is an assessment of the uncertainty. Guidance is based on documents andrecommendations prepared by the Joint Committee for Guides in Metrology (JCGM), which
gives definitions and guidance for metrology in general. These are available from the website
79

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of the Bureau International des Poids et Mesures: JCGM 200 (JCGM, 2008a), JCGM 100(JCGM, 2008b), and JCGM 104 (JCGM, 2009). These definitions and guidance are
published by the International Organization for Standards (ISO) and the International
Electrochemical Committee (IEC) (ISO/IEC Guide 99, 2007; ISO/IEC Guide 98-3, 2005;
ISO/IEC Guide 98-1, 2009).
(202) An essential aspect of quality assurance is assessing to what extent is it reasonable tobelieve that the reported number is a good estimate of the true dose value. The greater thisbelief, the confidence or probability that the measured value is within a certain defined range
around the true value, or rather that the true value is within a certain range of the observed
value, the better the quality of the measurement. In the evaluation of the uncertainty, allknowledge of the instrument and evaluating system both from experience and from type
testing should be used possibly in combination with detailed information on the instrument
assembly usage.
(203) In order to obtain dose data of which the quality is traceable and can be recognized itis recommended that the terms and definitions given in the documents issued by the JCGM
and the ISO framework should be followed. In the formulation stage, all input/influencequantities that may contribute to the uncertainty should be identified, and must be consideredin the measurement model; all model input/influence quantities should be characterized by abest estimate and either a probability density function (PDF) or a (combined) standard
uncertainty. The shape of the PDF can be taken from measured data or from an assigned
distribution. Results from a type test or other characterization of the response of a dosimetry
system may be used as inputs to the uncertainty assessment; other parameters such as
standard uncertainty and coverage intervals must be derived from the PDF of the output
quantity.
(204) ICRP in Publication 75 (ICRP, 1997) recommends that "In practice, it is usuallypossible to achieve an accuracy of about 10 % at the 95 % confidence level for measurementsof radiation fields in good laboratory conditions. In the workplace where the energy anddirectional distribution of the particles in the radiation field are generally not well known, theuncertainties of an assessment will be significantly greater. Non-uniformity and uncertain
orientation of the radiation field will introduce errors in the use of standard models. The
overall uncertainty at the 95% confidence level in the estimation of effective dose around therelevant dose limit may well be a factor of 1.5 in either direction for photons and may besubstantially greater for neutrons of uncertain energy, and for electrons. Greater uncertainties
are also inevitable at low levels of effective dose for all qualities of radiation.” Thesestatements of ICRP strictly apply to the assessment of E and HT for occupational exposure at
low doses on Earth. ICRU has published recommendations on the acceptable levels of total
uncertainty for dose measurements in radiological protection in Reports 47 and 66 (ICRU,
1992, 2001) which are broadly consistent with ICRP statements. ICRU recommends for
single measurements of the operational quantities that "....in most cases, an overall
uncertainty of one standard deviation of 30% should be acceptable" and states "The error of
instruments may substantially exceed this limit at some radiation energies and for certain
angles of incidence, but conform to it when they occur in a radiation field with a broad
energy spectrum and broad angular distribution".
(205) The statistical uncertainty of laboratory calibrations is commonly far less than theabove uncertainties. However, the absorbed-dose and dose-equivalent response of devices are
frequently appreciably energy- and angle-dependent. In order to minimize the total
uncertainty in practical measurements, either determination of the response is required for theradiation field in which it is to be used, or a simulation of this field may be used to determine
80DRAFT REPORT FOR CONSULTATION
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and apply correction factors to the calibration factor of an instrument. It may also be possible
to calculate the response in this field from the knowledge of the field and of the detailedenergy- and angle-dependence of response of the device. Frequently, it is the direction
distribution of the field which has the largest influence. For measurements in space,additional information on the particle type, energy and direction distributions, are available.
Using these data, accuracies of better than a factor of 1.5 at the 95% confidence level(equivalent to a standard deviation for a normal distribution of about 0.25) should beachieved for the estimation of organ absorbed dose and organ dose equivalent.
(206) At doses approaching or exceeding mission risk limits, or career risk limits, theupper 95% coverage probability is used to include the measurement uncertainty for theassessment of the cancer risk projections from estimations of organ doses and radiation
quality and tissue weighting factors (see Sect. 7.5). Obviously, reduction of measurement
uncertainties is seen to be an important task for mission planning.

5.

RADIATION FIELDS INSIDE SPACECRAFT AND ON
PLANETARY SURFACES(207) The radiation field inside or near spacecraft includes various components of the
primary radiation field in space (see Chapter 2) partially absorbed in the walls of thespacecraft and secondary radiation which is produced by scattering and reactions of the
primary radiation in the walls and other materials within the spacecraft. Due to both thevariation of the primary radiation field with time and to the non-homogeneous distribution ofmaterials within the spacecraft the internal radiation field depends on the position in thespacecraft and on time during the mission.
(208) The radiation field near planetary surfaces is determined by several factors, such as
the existence and strength of a magnetic field, the thickness and composition of theatmosphere and the planetary material near to the surface. Important are the scattering,absorption and reactions in the planetary atmosphere and in the ground material.
5.1

General(209) The physical description of the interaction of space radiation with matter requires
knowledge of the energy and isotopic distribution of primary and secondary charge particles
and neutrons produced in atomic and nuclear collision processes in the transport of radiation
through matter. Computer codes describing proton, high-energy and charge (HZE) nuclei,
and secondary radiation energy distributions and their transport through matter are used forshielding design of spacecraft and planetary habitats, and organ exposure assessments. The
codes need to be benchmarked against space dosimetry results. The broad range of ion types
and energies of the galactic cosmic radiation and solar particles, and the large number ofmaterials of interest in spacecraft structures, planetary atmospheres, and tissues require a
detailed description of the basic physical processes including the development of reliable
computer models. Studies of potential risk mitigation including operational, shielding, andbiomedical approaches must rely on theoretical models in the form of radiation transport
codes to make projections and to support design studies of such mission.
(210) Dominant physical processes in the penetration of high-energy nuclei through matterare energy loss through atomic and molecular collisions and the absorption and particle
production from nuclear interactions with spacecraft materials and tissue. For heavy ions with81

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high kinetic energies (> 100 MeV/u), nuclear absorption by fragmentation is the dominant
reaction mode (Hufner, 1985, Townsend et al., 1996). The nuclear absorption cross section
scales by the nuclear mass number to a power, A1/3 and fragmentation of GCR nuclei is more
efficient per unit mass for materials with light constituent atoms. At lower energies (<100MeV/u), elastic scattering, compound nucleus formation or excitations of discrete nuclear
levels that decay by gamma emission or particle emission are dominant interaction modes.
However, the short-range and large stopping powers of heavy ions reduce the importance of
nuclear reactions at lower energies except for neutrons. High-energy protons and neutronsinteract through knockout and spallation reactions (Hufner, 1985). Such processes lead to abuild-up of light particles (Z ≤ 2) and the localized production near the primary track ofheavy ion target fragments with large values of LET and short ranges (Wilson, et al., 1991,
Cucinotta et al., 1996).

2812

Ω φj(x,Ω,E)= Σk ∫∫ σjk(Ω,Ω',E,E') φk(x,Ω',E')dE'dΩ' - σj(E) φj(x,Ω,E)

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5.2

Physics of space radiation transport

5.2.1 Radiation transport(211) The description of the passage of high-energy nuclei through matter can be madeusing the Boltzmann transport equations that treat the atomic and nuclear collisions. The
equations may be solved by either numerical and analytic techniques - the straight ahead
approximation, or as an alternative, by Monte-Carlo techniques which sample frominteraction processes for individual primaries or their secondaries to develop histories ofcharged particle passage and energy deposition in materials. The Monte Carlo method is a
widely used technique in particle physics and often applied in simulating radiation transport
through matter and the calculation of dose distributions.
(212) The relevant Boltzmann transport equations are derived on the basis of conservation
principles (Wilson et al., 2001) for the fluence rate φj(x,Ω,E) of type j particles as:
'

(5.1)

'

where σj(E) and σjk(Ω,Ω ,E,E ) are the media macroscopic cross sections. The σjk(Ω,Ω′,E,E′)
represent all those processes by which the particles of type k moving in direction Ω′ withenergy E’ produce a particle of type j in direction Ω with energy E. The fluence rate
φj(x,Ω,E) is the main physical quantity used to determine the physical or biological response
by folding it with an appropriate response function for the physical or biological system
under study.
(213) There may be several reactions, which produce a particular product, and theappropriate cross sections for Equation (5.1) are the inclusive ones. The total cross section
σj(E) with the medium for each particle type of energy E may be expanded as:
σj(E) = σatj(E) + σelj(E) + σrj(E) ,(5.2)

where the first term refers to collision with atomic electrons, the second term is for elastic
nuclear scattering, and the third term describes nuclear reactions. The microscopic crosssections and average energy transfer are ordered as follows:2826

σatj(E) ~ 10-16 cm2with δEat ~102 eV

(5.3)

2827

σelj(E) ~ 10-19 cm2with δEel ~106 eV

(5.4)

2828

σrj(E) ~ 10-24 cm2with δEr ~108 eV .

(5.5)

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Over a distance of 1 g cm-2 of a material many atomic collisions (~ 106) occur, many lessnuclear coulomb elastic collisions (~ 103) , while nuclear reactions are separated by up to
many cm depending on energy and particle type. For neutrons, it is σatn(E) ~ 0 and thenuclear elastic process appears as the first-order perturbation. Mean free paths for elastic
scattering of neutrons may become quite small, especially at low energies in the resonanceregion (ICRU, 2000).
(214) The solution of Equation (5.1) involves hundreds of multi-dimensional integrodifferential equations which are coupled together by thousands of cross terms and must be
solved self-consistently subject to boundary conditions that ultimately relate to the external
environment and the geometry of the astronaut's body and/or a complex spacecraft. A seriesof approximate solutions can be studied and indicates a high level of accuracy for mostapplications (Wilson et al., 2001, Tweed et al., 2005). The mean energy loss can be
introduced in a continuous slowing down approximation (csda), and straggling neglected forthe broad energy spectra of the space radiation. The highly directional coulomb cross section
for charged ions (Wong et al., 1990) and nuclear elastic scattering for neutrons generally
dominate the second perturbation term. The angular dispersion and its effects on lateral beam
spread and range straggling are important corrections in comparing to laboratory
measurements. The nuclear elastic scattering is especially important to neutron fields and has
been treated using Monte Carlo or multi-group methods (Hughes, et al., 1997). The third
perturbation term consists of complex energy and angle functions. Results from Monte Carlocodes (Allsmiller et al., 1965) provided the basis for the generation of analytical techniques
and the simplification of boundary conditions used in space shield code development (Wilson
et al., 1991).

2861

Sn(E) = ΣiΣl εni σi (E) ,

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where εi is based on the electronic excitation energy, and σi(E) is the total atomic/molecularcross section for delivering εi energy to the orbital electrons (including discrete andcontinuum levels). The first moment (n=1) is the usual stopping power, and the usual
continuous slowing down approximation (csda) is achieved by neglecting the higher-energy
moments. The second moment represents the energy straggling (Payne, 1969) due to thestochastic distribution of energy loss.
(216) Stopping power data bases are derived semi-empirically as the Bethe reduction of
Equation (6) in terms of mean excitation energies and shell corrections (Fano, 1963, Wilson
et al., 1991). The stopping power, S, is adequately described by the Bethe-Bloch formula formost ion energies (Bichsel, 1992):

2872

(5.7)

5.2.2 Atomic processes.
(215) The transport coefficients describe the atomic/molecular and nuclear processes bywhich the particle fields are modified by the presence of material (Wilson et al., 2001). As
such, basic atomic and nuclear theories provide the input to the transport code databases. The
first order physical perturbation on the right side of Equation (5.1) is the atomic/molecularcross sections as noted in Equation (5.3) for which those terms in Equation (5.1) are
expanded about the energy moments l as

83

(5.6)

DRAFT REPORT FOR CONSULTATION
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where e is the electronic charge, NT is the density of target atoms, m is the mass of theelectron, c is the speed of light, β=v/c, and I is the mean excitation energy. In Equation (5.7),
the various terms are the shell correction C(β), Barkas correction, L1(β), Bloch term, L2(β),
and Mott and density corrections L1(β). The range of the ion is evaluated from the stopping
power asEdE´S ( E´)
0

R( E )  

2878

(5.8)

2879
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(217) The second energy moment is related to energy or range straggling and provides
corrections to the ion slowing down spectrum (Fano, 1963, Payne, 1969). For broad-energy
beams conditions of GCR or SPEs transport straggling effects are negligible, however they
are important for laboratory studies with mono-energetic beams and for understanding
radiation detector response. The next physical perturbation term is the Coulomb scattering by
the atomic nucleus and is typically represented by Rutherford scattering modified byscreening of the nuclear charge by the orbital electrons using the Thomas-Fermi distribution
for the atomic orbits. The total nuclear Coulomb cross section found by integrating over the
scattering directions is related to the radiation length. The differential cross section is highly
peaked in the forward direction, and only after many scatterings is significant beam
divergence seen. Numerical solutions to the Coulomb multiple-scattering problem have been
investigated for many years (Fermi, 1940) and accurately describe experimental data with
HZE (Wong et al., 1990) or proton beams (Carlsson and Rosander, 1973).

2909
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where q is the momentum transfer, and k the relative momentum of projectile and target
nuclei.
(219) The total absorption (ABS) cross section is then also found from the elastic
scattering amplitude by using:TOT = ABS+EL(5.10)
where σEL is the total elastic cross section. Formula for these cross sections can be derived
from microscopic theories of nuclear multiple scattering (Cucinotta et al., 1997). The
absorption cross sections are accurately represented by energy dependent variants of the
Bradt-Peters equation (Townsend et al., 1986a)

5.2.3 Nuclear interactions(218) The extent of the nuclear interaction cross section database required for the transportof cosmic radiation is for energies from 1 MeV/u to energies of tens of GeV/u, including alarge number of projectile and target material combinations. The types of cross sections
required for transport involve total yields and multiplicities and inclusive secondary energy
spectra, inclusive double differential cross sections in angle and energy. The total absorption
plays a critical role in ensuring a reasonable solution to the Boltzmann equation including theaccuracy of particle conservation as a function of depth in the shield (Wilson et al., 1991).
Similarly in Monte-Carlo approaches the absorption cross section plays the critical role ofdetermining the probability of interaction events along the trajectory of a primary particle inthe shielding. In addition, exclusive cross sections are used in some event generators inMonte-Carlo transport codes. The total cross section σTOT is found from the elastic amplitudein the forward direction as found in the optical theorem (Wilson et al., 1991) as the imaginary
part of the elastic scattering amplitude (Im f):
 TOT 4Im f (q  0)
k

(5.9)

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2944
2945

 ABS  r02 c1 ( E )( Ap1 / 3  AT1/3  c2 ( E )) 2

(5.11)
where r0, c1(E) and c2(E) are parameters fit to experimental data. Absorption cross sections
have been well studied both experimentally and theoretically and are known with a few
percent uncertainties (Tripathi, 2001). The absorption cross section rises at low energy asreaction channels open and reaches a minimum at a few hundred MeV/u before rising again
as meson production channels open.
(220) Table 5.1 shows reaction partners and secondaries of relevant reactions broken into
distinct reaction types or mechanisms. Low energy evaporation products including heavy ion
target fragments are high-LET events important in biological damage. Knockout products
from proton or neutron reactions and projectile fragments from nuclei of GCR are typicallyof low to moderate LET, however, their large ranges leads to radiation build-up throughfurther reactions. The abrasion-ablation models (Hufner et al., 1975, Towsend et al., 1986b,
1996, Wilson et al., 1995b, Cucinotta, et al., 1997) are used to describe heavy ion
fragmentation cross-sections. The description of nuclear reactions through abrasion (particle
removal during ion-ion interaction) and ablation (nuclear de-excitation after the abrasionstep) is illustrated in Fig. 5.1, which shows the roles of projectile overlap, fireball formationin central regions, and the decay of the pre-fragment spectators (NCRP, 2006). The
individual steps of abrasion and ablation can be described in both semi-classical or quantum
mechanical approaches (Cucinotta et al., 1995; 2007). These different reaction processes
have been described by quantum multiple scattering theories (QMST), semi-classicalmethods such as quantum molecular dynamics, or Monte-Carlo approaches to nuclear
reactions using an intra-nuclear cascade model (see Durante and Cucinotta, 2011 andreferences therein for a review of nuclear reaction models).

Fig. 5.1

85

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2956
2957

Fig. 5.1a. Schematic diagram of the reaction of an incident nucleon with a target nucleus at highenergies (ICRU, 1978).

Fig. 5.1b. Schematic diagram of a relativistic heavy ion reaction with a target nucleus (Miller, 1997).

Table 5.1.

Reaction products in nuclear reactions important to space radiation studies.

REACTION
TYPE

SECONDARYMECHANISMCOMMENT

Nucleon-Nucleus

NucleonEvaporation
Knockout and elastic,
quasi-elastic scattering

High LET, small range
Large range

Nucleon-Nucleus

Light particle(d,t,h,α)Evaporation
Knockout, pickup

High LET, small range
Large range

Nucleon-Nucleus

Heavy recoil

Elastic scattering
Fragmentation or
spallation

High LET, small range
High LET, small range

Nucleus-Nucleus

Nucleon or lightparticle

Target or projectile
Knockout or evaporation

Small LET, large range
High LET, small range

Nucleus-Nucleus

Heavy ion

Projectile Fragment

Mod. LET, large range

Nucleus-Nucleus

Heavy ionTarget Fragment

High LET, small range

Nucleon or
Nucleus-Nucleus

Pion, Kaon, antinucleon, gamma

Target reaction
Proj. E > 500 MeV/u

Deep penetration(> 50 g/cm2)(221) Examples of fragmentation cross sections for Ar and Fe projectiles are shown in Fig.
86

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5.2 in comparison to the quantum multiple scattering fragmentation (QMSFRG) model(Cucinotta, et al, 2002, 2006b, and 2007). Available fragmentation cross section data sets fortarget atoms of interest for space missions were reviewed by Durante and Cucinotta (2011)
and NCRP (2006). One feature of the elemental distribution of the fragments is the strong
even-odd effect in the charge number of the fragments observed. The effect appears to belargest for intermediate mass projectiles (A=20 to 40) and depends on the isospin of the
projectile (Knott et al., 1996, 1997). Theoretical models provide a good representation of the
odd-even effect if accurate nuclear de-excitation models are used (Cucinotta et al., 2002,
2006b, 2007). Figure 5.2 shows comparisons of fragmentation production cross sections of
the QMSFRG model with experiments for several beam energies of 56Fe interacting with avariety of target nuclei. Good agreement between experiments and the QMSFRG model
within 25% for most fragment cross sections has been achieved as shown in Fig. 5.3. A larger
data base for cross sections for proton and neutron induced reactions now exits with recent
surveys of such data provided in ICRU Report 63 (ICRU, 2000). Above kinetics energies of afew 1000 MeV/u, multiple meson production processes are dominant and reactions models
based on patron or quark-gluon models can be used to describe nuclear interaction crosssections (Fasso et al., 2005).
12 1240Ar +
C

56Fe
56 + 1212C(0.6
GeV/u)
A r+ C (0.6
G eV
/u)

(0.6GeV/u)
GeV/u)
Fe+ C (0.6
QMSFRG
Experiment

Q M S FR G
E xperim ent

100 F, m b

 F, m b

100

10

10

1

1

0.1

0.1

24

C

C

ha

17
16
15
14
13
12
11
10

rg

e,

ZF

9
8

2975
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2979

38

36

34

32

30

28

26

ss
Ma

24

22

20

18

16

14

ha 22 20
rg
e, 18
ZF
16

36

28

24

20

40
44
14

, AF

32

48
52

Ma

ss,

AF

Fig. 5.2. Comparisons of the QMSFRG model (Cucinotta et al., 2006b) to experiment for isotopic
distribution of fragments for 40Ar on 12C at 0.6 GeV/u (left panel) and 56Fe on 12C interactions at 0.6
GeV/uFig.(rightpanel).
5.2

87

DRAFT REPORT FOR CONSULTATIONF(QMSFRG), mb

0.65 GeV/u

1.05 GeV/u

1.6 GeV/u

H
C
Al
Cu
Pb
One-to-One
+25 %

102

102

102

2980
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2988

F (measured), mb

102

F (measured), mb

F (measured), mb

Fig. 5.3. Comparisons between experiments and the QMSFRG model for fragmentation crosssections for 56Fe projectiles of different energies interacting with several target nuclei (Cucinotta etal., 2006b) where the dashed lines show ±25 % ranges of the experimental data.

(222) The momentum distribution of heavy projectile fragments is forward peaked anddescribed as a Gaussian distribution in the projectile rest frame with a small downshift in the
average momentum from the projectiles velocity. The longitudinal momentum width, L, iswell described by (Goldhaber, 1974): n( Ap  n) L 0 Ap  1 

2989
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3001
3002
3003
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3006
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3009
3010
3011
3012
3013

102

1/ 2

(5.13)

where n is the number of nucleons removed from the projectile and σ0 is approximately
related to the Fermi-momentum of the projectile, pF, by σ0= pF/√5. The transverse width isapproximately the same as the longitudinal for heavier fragments. A small momentum
downshift of the fragments relative to the projectile also occurs and is dependent on the
fragment mass (Tull, 1990). Transformation of the Gaussian distribution to the laboratory rest
frame reveals a narrow angular distribution for the projectile fragments that are strictly
forward peaked in a narrow cone (<5°), which leads to the success of the straight-ahead
approximation in transport models. For lighter fragments the longitudinal and traverse widths
diverge and the Gaussian model breaks down. This is due to the multiple sources for lightparticle production including projectile abrasion, projectile ablation, target abrasion, andtarget ablation, as well as a possible intermediate source due to the formation of anintermediate rapidity fireball in central collisions.
5.3

Proton, neutron and heavy ion transport codes(223) Several radiation transport codes have been developed for applications inradiotherapy, physical experiments at high-energy accelerators, detector simulations, andradiation protection in space. The different radiation transport codes utilize distinct nuclear
data bases and methods including their treatment of nuclear interactions, secondary radiation,and shielding geometries. It is unlikely that space radiation problems can be handled with aone-size fits all approach and the specific application will drive the method to be used.
Complex spacecraft and organ geometry are described using ray-tracing distributions,combinatorial geometry models of complex structures, or voxel based methods. Ray tracing
methods are able to treat thousands of spacecraft parts accurately and can directly integrate88DRAFT REPORT FOR CONSULTATION
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engineering designs in a CAD format. Ray tracing methods have only been developed for bidirectional (forward-backward scattering); however they have been shown to be quite
accurate for the omni-directional radiation fields in space. Combinatorial geometry models,often used by Monte-Carlo codes, rely on approximations that paradoxically wash out thefine details of surface and angular effects that 3D-transport models are intended to describe.
(224) Models of the GCR, trapped radiation or SPE’s are usually used as the boundary
condition for transport codes. Several transport codes used in space applications are briefly
summarized here:

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(225) FLUKA is a general purpose Monte Carlo program for calculations of particle andphoton transport (Fassò et al., 2005; Battistoni et al., 2006) which can simulate theinteractions and propagation in matter of approximately 60 different particles, including
heavy ions (http://www.fluka.org). The program can also describe the transport of polarised
photons (e.g., synchrotron radiation) and optical photons. Photonuclear interactions can be
simulated. Time evolution of the radioactive nuclei inventory and tracking of emitted
radiation from unstable residual nuclei can be performed.
(226) Depending on the energies of the primary particles, hadronic interactions are
simulated by different physical models. For higher energies, the Dual Parton Model is used.
Below 3-5 GeV/c the PEANUT package includes a very detailed Generalised Intra-Nuclear
Cascade (GINC) and a pre-equilibrium stage, while at high energies the Gribov-Glauber
multiple collision mechanism is included in a less refined GINC. Nuclear interactions
generated by ions are treated through interfaces to external event generators, except for the
low energy (less than 150 MeV/u) range, for which a model based on the Boltzmann Master
Equation (BME) has been implemented. The RQMD (Relativistic Quantum Molecular
Dynamics) generator is invoked from 100 MeV/u to 5 GeV/u, and the DPMJET code is used
for energies over 5 GeV/u.
(227) The transport of charged particles is described by applying a multiple scattering
algorithm based on Moliere’s theory of Coulomb scattering. The algorithm includes anaccurate treatment of curved trajectories in magnetic fields. The energy loss is determinedaccording to the Bethe-Bloch theory and from bremsstrahlung and pair production. Ionisation
fluctuations are accounted for.
(228) For neutrons with energies lower than 20 MeV, FLUKA employs a multi-grouptransport algorithm, which uses a subdivision of the neutron energy range in 260 groups andis based on neutron cross section libraries containing more than 200 different materials,
selected for their use in physics, dosimetry and accelerator engineering. Energy depositions
for nuclei other than hydrogen are calculated by kerma coefficients.
(229) FLUKA can handle very complex geometries, using an improved version of thewell-known Combinatorial Geometry (CG) package. Repetitive structures (lattices) and voxel
geometries can be handled. Various visualisation and debugging tools are also available.

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(230) The Monte-Carlo code Geant4 (Agostinelli, 2003 and Allison, 2006) states for
GEometry ANd Tracking and is a software toolkit for simulating the passage of particles
through matter. It has been developed and maintained by the Geant4 Collaboration which is aworldwide
teamworkofphysicists
andsoftwareengineers(see:
http://geant4.web.cern.ch/geant4). Geant4 and its predecessors were designed to utilise the

FLUKA (FLUctuating KAscades)

GEANT489

DRAFT REPORT FOR CONSULTATION
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physics models, to handle complex geometries, and to enable its easy adaptation for optimal
use in different sets of tasks. It has its applications in high energy, nuclear and accelerator
physics as well as studies in radiation protection, medical and space science.
(231) The toolkit includes facilities for handling tracking, geometry, physics models,detector response, run management, visualisation and user interface. The software offers alarge set of physical processes (e.g. electromagnetic, hadronic and optical model), different
type of particles (leptons, bosons, mesons, baryons, etc) and databases with properties ofmatter and elements. Physics processes cover a wide range of energies which spans from 250
eV up to TeV depending on the case. Several of the modules contained in Geant4 are recreations of physics in other codes including e. g. HZETRN, HETC. Spacecraft geometry
models are available including multi-layered shielding simulation Software (MULASSIS)(Bernabeu and Casanova, 2007).
(232) The toolkit is implemented in C++ programming language making use of object
oriented technique. This approach allows users effectively to manage complexity and limit
dependencies by defining a uniform interfaces and common organisational principles in orderto create an application for solving a specific problem.

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(233) HETC is a high energy Monte Carlo radiation transport code and was developed at
Oak Ridge National Laboratory (Townsend et al., 2002). The code was originally developed++
for transport calculations with incident high-energy
only.
Lateron Townsend et al. (Townsend et al., 2005) have extended the model especially forspace radiation shielding applications. The code, now called HETC-HEDS, has been
modified to include the transport of heavier nuclei (Charara et al., 2008).
(234) HETC-HEDS includes nucleus-nucleus cross sections, range-energy tables scaled
from the proton data, and a nuclear collision module for heavy ion interactions. Nonelastic
nucleon collisions and charged-pion collisions with hydrogen at energies above 3.5 GeV and
2.5 GeV, respectively, are treated by using calculational methods that utilize experimental
data for the total non-elastic n-p, p-p, +-p cross sections and analytic fits toexperimental data. The intra-nuclear-cascade evaporation concept of particle-nucleus
interaction is used to determine the effect of particle-nucleus collisions below 3.5 GeV for
nucleons and 2.5 GeV for charged pions. Following the intranuclear-cascade, the excitationenergy left in the nucleus is treated using an evaporation model. The particles allowed during
evaporation include protons, neutrons, d, 3H, 3He, and 4He.
(235) HETC-HEDS used the combinatorial geometry package so virtually arbitrarygeometries are allowed. Each particle in the cascade is followed until it eventually disappears
by escaping from the geometric boundaries of the system, undergoes nuclear collision orabsorption, comes to rest due to energy losses from ionisation and excitation of atomic
electrons, or decays in the case of pions and muons.

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(236) HZETRN was developed by Wilson et al. (1991, 2004) at NASA. It solves theBoltzmann equation using numerical methods. The early version used the straight-ahead
approximation but more recent versions use bi-directional transport or 3D transport forlaboratory studies (Wilson, et al., 2009). Recently ray tracing representations of voxel models
of human geometries have been developed (Slaba et al., 2009). Nuclear interactions aretreated by the NUCFRG2 Model (Wilson et al., 1994a) or QMSFRG model (Cucinotta et al.,HETC-HEDS (High Energy Transport Code-Human Exploration)

HZETRN (High charge (Z) and Energy Transport code)90DRAFT REPORT FOR CONSULTATION
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2007) with proton and neutron cross sections described by the Bertini and Ranft models. To
treat complex radiation geometries ray tracing methods are utilized, which is powerful
because spacecraft engineers can utilize their designs directly in the transport codeevaluations. Computer runs on small computer workstations can be performed in less than
one hour for complex spacecraft geometries with multi-layer materials and deep shielding
conditions (>100 g/cm2) combined with models of the organ shielding of the human body.

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(237) The Los Alamos Monte-Carlo code MCNPX (see: http://mcnpx.lanl.gov) and its
predecessors are very widely distributed (Waters, 2002; Pelowitz, 2008).The code is capableof tracking many particle types (nucleons and light ions) and over 2000 heavy ions up to very
high energies. It uses standard evaluated data libraries for neutrons, photons, electrons,
protons and photonuclear interactions and uses physics models for other particle types and atenergies for which tabular data are not available.
(238) Current physics modules include the Bertini and Isabel models taken from the
LAHET Code system, CEM 03, and INCL4 (James et al., 2009). The incorporation of aheavy ion physics model has enabled the transport of recoil nuclei. This model automaticallytransports all residuals that are produced from any reaction even if the source particle is not aheavy ion. Current stopping powers for heavy ions have been adjusted in an ad hoc fashion(Pelowitz, 2008) so that they better match SRIM results (Ziegler et al., 2008). Charged
particles are slowed down to a lower total energy limit of 5 MeV, at which point theirremaining energy is locally deposited.

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(239) The Monte-Carlo radiation transport code PHITS (see: http://phits.jaea.go.jp) was
developed under collaboration with several institutes including JAEA, RIST, KEK and
Chalmers University of Technology (Niita et al., 2010; Sihver et al., 2010a). Nuclear
interactions are described by various models such as JAM and JQMD up to 100 GeV/u. The
code can determine the energy of charged particles emitted from low-energy neutron-induced
nuclear reactions, using the event generator mode (Iwamoto et al., 2007, Niita et al., 2007) incombination with nuclear data libraries. This feature enables the direct calculation of dose
equivalent in organs or tissues which cannot be calculated by employing the conventional
kerma approximation. The accuracy of the code for use in space dosimetry was well verified
by calculating neutron spectra inside Space Shuttle (Sato et al., 2006) and doses inside
anthropomorphic phantoms (Sato et al., 2011), using simplified geometries of spacecraft. The
code is also used for the computational analyses of the MATROSHKA and MATROSHKAR experiments in space (Sihver et al., 2010b and Koliskova et al., 2012).

MCNPX (Monte-Carlo N-Particle eXtended)

PHITS (Particle and Heavy-Ion Transport code System)

5.3.1

Inter-comparison and validation of radiation transport codes(240) An assessment of the accuracy of space radiation transport models for prediction ofenergy spectra of charged particles and neutrons after primary radiation has passed matter canbe made by comparisons to laboratory experiments with proton and heavy ion beams or frommeasurements in spacecraft. Spaceflight measurements, however, involve many factors suchthat potential inadequacies in radiation transport models are difficult to isolate relative topossible inaccuracies in environmental or shielding models. Also, space validation is limitedby the access to space and current spacecraft materials, and may not be representative of91

DRAFT REPORT FOR CONSULTATION
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model predictions for other material types such as those that occur on planetary surfaces or inadvanced materials selection concepts. In this respect, laboratory validation is advantageous
to validate radiation transport computer codes and associated data base models and to provide
tests for studying material properties for reducing biological doses (Schimmerling et al.,1999). Nevertheless, spaceflight measurements provide important tests of predictive
capability of several factors and are needed for final validation of transport codes.
(241) Recently an extensive benchmarking of the calculated projectile fragmentation
cross-sections from the reactions of 300 - 1000 MeV/u Si-28, Ar-40, and Fe-56 ions onpolyethylene, carbon, aluminum, and copper targets (relevant to space radiation protection)
has been carried out using PHITS, FLUKA, HETC-HEDS, and MCNPX. Calculated results
were compared with measurements (Sihver et al., 2008).
(242) An over-all “reasonable” agreement between calculations and measurements wasfound. However, a general trend of a slight underestimation of the calculated fragment
production cross-sections (partial charge-changing cross-sections) has been observed. The
code HETC-HEDS seems to underestimate these cross-sections more than the other codes
included in this benchmarking. PHITS also seems to underestimate the total charge-changing
cross-sections, which is in agreement with other observations (Sihver et al., 2007).
(243) A recent inter-comparison of transport codes for SPE and GCR test cases indicates
fairly good agreement between the various codes (Wilson et al., 2009; Heinbockel et al.,2011). Fig. 5.4 shows comparisons of results of depth-dose distributions from different codes
for a large SPE. Fig. 5.5 shows a comparison of energy spectra of secondary particles
produced by protons and Helium ions of GCR at solar minimum calculated with various
codes.

92

DRAFT REPORT FOR CONSULTATION
3179
HETC-HEDSPHITSGEANT4FLUKA
HZETRN

Absorbed dose / mGy

Absorbed dose / mGy

HETC-HEDSPHITSGEANT4FLUKA
HZETRN

Depth / g cm-2

HETC-HEDSPHITSGEANT4FLUKA
HZETRN

Dose equivalent / mSv

HETC-HEDSPHITSGEANT4FLUKA
HZETRN

Dose equivalent / mSv

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Depth / g cm-2

Depth / g cm-2

Depth / g cm-2(a) Aluminum shielding(b) Iron shielding

Fig. 5.4. Inter-comparison of transport codes for depth-dose distributions of absorbed dose and dose
equivalent from solar particle events in aluminum and iron shielding (Wilson et al., 2009).

93

DRAFT REPORT FOR CONSULTATION
103

108

104

101

10-4 -2
10

1

102

104

108
104
100
10-4

10-2

1

102

104

108

dΦE/dt / (cm2 MeV y)-1dΦE/dt / (cm2 MeV y)-1

100
10-3
10-2
3
10

1

102

104

105

1

102

104

105

101

10-3

10-2

103

104
101
100
10-4

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10-2

1

102

Particle energy

104

10-3
10-2

/ MeV u-1

1

102

104

Particle energy / MeV u-1a) GCR protonsb) GCR helium ionsFig. 5.5. Inter-comparison of energy spectra (spectral fluence rate, dΦE/dt) of light ions from GCR
at solar minima calculated by different transport codes (Wilson et al, 2009).
 HETC-HEDS, ▲ Fluka, ,  HZETRAN2006

5.4

Radiation Fields inside spacecraft(244) Radiation fields inside spacecraft are determined by the external radiation incident
on the spacecraft and the secondary radiation produced by the interactions with the walls andthe equipment inside and outside the spacecraft. The internal radiation field varies with time
due to the variation of the external radiation (see Chapter 2) and with the location in thespacecraft due to the specific arrangement of the equipment and the shielding properties ofthe different walls and spacecraft components. Important effects are absorption, scattering,and degradation of the primary radiation, and production of secondary radiation. Hence theradiation field inside a spacecraft –and also in the outer region near to the spacecraft –includes projectile and target fragment, neutrons, photons, pions and muons in addition to theradiation components of the primary field. Assessment of the inner radiation field and its
components can be performed either by measurements or by simulations using environmental
models and radiation transport codes.

94

109

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108

107

107

L d /dL / cm-2

L d /dL / cm-2

DRAFT REPORT FOR CONSULTATION

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105

104
103
102

101
10-1

3207

(a)

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101
10-1

103

L / keV mm-1

100

101

102

103

L / keV mm-1

(b)

109
Fig. 5.6aFig. 5.6b

L d /dL / cm-2

108

107
106
105

104
103
102

101
10-1

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(c)

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102

103

L / keV mm-1

Fig. 5.6. LET
distribution of particle fluence in space calculated using the HZETRN code forFig. 5.6cincreasing amounts of liquid hydrogen, water, and aluminum shielding (Wilson et al., 1995c).
○ without shielding; with shielding thickness of □ 5 g cm-2, ∆ 15 g cm-2,  30 g cm-2.

(245) The exterior environment is modified by the types and amounts of radiation
shielding. The LET distributions of particle fluence for increasing amounts of liquidhydrogen, water or aluminum shielding are shown in Fig. 5.6. The higher fluence at large
values of LET (>50 keV/mm) for aluminum compared to the other materials is due to thecontributions of secondary neutrons and charged particles produced in the shielding, which is
reduced for materials containing hydrogen.
(246) The measurements on NASA space shuttle (STS) flights over many years and on the
Russian space station MIR have allowed for a large number of comparisons of radiationtransport calculations to flight measurements (Cucinotta et al., 2000b). Passive measurementswith nuclear etched track detectors (PADC) have limitations at both low LET (< 5 keV/μm)
tracks and short-tracks from target fragments or stopping GCR ions of high-LET tracks. The
use of active dosemeters on STS flights has allowed for separation of GCR contributions
from that of trapped protons which is not possible with passive dosimetry (Badhwar andCucinotta, 2000). Active detector measurements include tissue equivalent proportionalcounters, charged particle telescopes (Badhwar et al., 1995), and active Bonner spheres
embedded with proportional counters (Koshiishi et al., 2007).

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Particle radiance / (cm2 s sr)-1

DRAFT REPORT FOR CONSULTATION
10-3
10-4
10-5

10-6
10-7
10-8
100

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LET spectra
CR-39 calculated△ CR-39 measured

101
102
103
LET / keV mm-1

104

Fig. 5.7. Comparisons of LET distributions of particle radiance measured by nuclear etched track
detectors (CR-39) to LET distributions and model calculations of LET distributions on Space shuttle
mission (Wilson et al., 1994b, Shinn et al., 1998).

(247) Measurements on STS flights were performed by Badhwar et al. (2000) using acylindrical tissue equivalent proportional counter (TEPC) with a length-to-diameter ratio of 1
simulating a 2 μm diameter site and covering a lineal energy range of 0.25 keV/μm to 1250
keV/μm. TEPC measurements on several missions in space have been compared to
calculations using HZETRN for total dose and dose equivalent. The comparisons use the freespace GCR model of Badhwar and O’Neill (1992) and representations of the STS or Mirshielding distribution around the detectors. The difference is found to be less than 15% for
the majority of the comparisons. A comparison of LET distributions measured by PADC andcalculated using the HZETRN code is shown in Fig. 5.7. They show a good agreement when
the response of the PADC to short tracks is additionally considered (Wilson, et al., 1994b,
Shinn et al., 1998).
(248) Particle energy distributions measured on STS-48 are shown in Fig. 5.8. Charged
particle telescopes are used which provide measurements of the energy spectra of lightparticles from about 15 MeV to 400 MeV for protons and other Z=1 and Z=2 ions from
5 MeV to 70 MeV/u (see above). These measurements are strictly secondary radiation due tothe Earth’s geomagnetic cut-offs, which exclude particles below a few hundred MeV/u fromentering the spacecraft orbit. Excellent agreement with the HZETRN code for protons isfound. For deuteron spectra the agreement is satisfactory only when knockout deuterons fromproton and neutron induced reactions are included. For 3He and 4He the agreement is lesssatisfactory, and may point to a deficiency in the evaporation cross sections of the FLUKA
model used by HZETRN.
(249) Detailed simulations of the radiation environment in the ISS from trapped proton
radiation have been performed by Wilson et al. (2007) using the HZETRN code and Ersmark
et al. (2007) using the Geant4 code. The anisotropy of the radiation field due to variation inshielding has also been studied.

96

DRAFT REPORT FOR CONSULTATION
1.6

A

Spectral radiance / (cm 2 s MeV sr)-1

Spectral radiance / (cm 2 s MeV sr)-1

8STS-48
GCR

7

B
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4

3
2

1
0

0

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400

A
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1.0

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0.6

B
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60

80

Deuteron energy / MeV u-1

Proton energy / MeV

(a)

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STS-48
GCR

1.4

(b)

Fig. 5.8. Comparison of calculated (HZETRN code) and measured energy distributions ofsecondary protons (a) and deuterons (b) from GCR during STS-48 (Badhwar et al., 1995). Calculated
proton and deuteron radiance (A) including knockout particles from proton and neutron induced
reactions, (B) without those contributions.

5.5

Radiation Shielding(250) Shielding models are applied for the spacecraft and spacesuits and allow evaluationof the interior environment to which the astronauts are exposed. The models describe the
distribution of materials in the walls of and within the spacecraft and appropriatecomputational procedures are used to evaluate the interior field of transmitted particles. Theinternal environment, especially which based on protons from the SAA, shows a nonhomogenous distribution with large spatial gradients and variations with time over both
short-term and long-term temporal scales.
(251) With the exception of the absolute intensity of the trapped environment and possible
solar particle events, the interior radiation environment can be well described using
computational models. High-speed computational procedures allow rapid mapping of theinteriors of the spacecraft.
(252) The interior environment of the spacecraft is also monitored by various instruments,
which can be used to adjust the trapped-particle intensity, reduce the uncertainty in the model
estimates, evaluate transmission factors, and evaluate calculated dosimetric quantities.
(253) Materials with light constituent atoms, such as hydrogen are most efficient per unit
mass of material at slowing down ions, attenuating heavy ion projectiles through projectile
fragmentation, and minimizing the build-up of neutrons and other target fragments produced
directly from the shielding by nuclear interaction. Energy loss through ionisation is
proportional to the number of electrons per atom (Z/A) where Z is the charge number and A
the mass number, and the energy loss per unit mass is proportional to (Z/ρA) where ρ is thedensity of the material. For the GCR, materials such as aluminum (the most common
spacecraft material) have relatively flat depth-dose equivalent responses due to the build-up
of light particles in balance with the attenuation of heavy ions (Wilson et al., 1995a).
Materials, such as concrete or lead, have a response to the GCR that is predicted to increase
the dose with shielding depth because of the large production of neutrons and target

97

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Aluminum

Water

Polyethylen
Liquid hydrogen

0

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Dose equivalent rate / mSv d-1

fragments. Spacecraft materials are often deficient in hydrogen and therefore neutron spectra
will change appreciably in the first few cm of tissue as low-energy neutrons (< 5 MeV) areproduced more frequently compared to aluminum or other common spacecraft materials.
(254) For a given area density and a given incident charged particle, ionisation energy loss
increases with the charge-to-mass ratio of the target nucleus (ZT/AT), while the fragmentation
cross section per unit mass is proportional to AT-1/3. Hence, hydrogen is the most efficientmaterial for shielding against heavy ions, and materials abundant in loosely bonded hydrogenatoms are excellent candidates for efficient radiation shielding.

Dose equivalent rate / mSv d-1

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20

30

40

50

Aluminum

Polyethylen

Liquid hydrogen
0

Depth in/ gg/cm
cm-22
Depth

Water

10

20

Depth

30

40

50

/ g cm-2

Fig. 5.9. Calculated dose equivalent rate in tissue versus shielding thickness for different shielding
materials in the ISS orbit for GCR and trapped protons and solar minimum conditions (Cucinotta etal., 2000b)(255) Having just one shielding material is an ideal case, which will in practice be very
hard to realize. The final shielding effectiveness will therefore also depend on the geometry
and theabundance of the various other materials used in the shielding. Ultimately, detailed
Fig. 5.5
5.8
simulations will always be mandatory in evaluating and designing a realistic spacecraft or
habitat. Simulations suggest that shielding is effective against trapped protons in LEO, but its
efficiency is poor against GCR penetration. This is demonstrated clearly in Fig. 5.9.
(256) In case of thicker shields, the neutrons, which as primary components of spaceradiation are negligible, can become a noticeable source of radiation exposure. This occurs
not only in heavier shielded spacecraft but also on planetary or lunar surfaces which lack an
atmosphere thick enough to attenuate the primary radiation source to a reasonably low level.
On the surface of Mars and even more so of the Moon, these secondary “albedo” neutrons
emerging from the ground contribute significantly to the overall exposure, in particular, since
neutrons are high-LET radiation with a high radiobiological effectiveness.
(257) There is an immense body of work already done in developing shielding strategies
for human space exploration missions. This activity resulted in numerous workshops andpublications in this field (Wilson et al., 1995a; Durante and Cucinotta, 2011). As mentioned
above, all calculations and measurements show that hydrogenous materials are the best
candidates per unit mass basis. The next set of figures (Fig. 5.10) taken from Wilson et al.
(2001) shows this clearly for cosmic ray spectra on Moon and Mars and a worst-case SPE.

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
 
•
••

Upper lines: 1977, min. solar activity
Lower lines: 1990, max. solar activity

300

200

100

0

0

25

50

75


 
•
••

300

Al-2219
Polyethylene
Hydrogeneded N-absorber
Liquid hydrogene

Upper lines: 1977, min. solar activity
Lower lines:1990, max. solar activity

200

100

0

100

Sphere thickness / g cm-2

3326
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0

25

50

75

100

Sphere thickness / g cm-2(a) GCR at the Moon (left) and Mars (right)

Dose equivalent / mSv

100 Al-2210
   Polyethylene Hydrogeneded N-absorber Liquid hydrogene

800

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0

0

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Dose equivalent / mSv

950

Fig. 5.9a

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Al-2219
Polyethylene
Hydrogeneded N-absorber
Liquid hydrogene

Annual dose equivalent / mSv

Annual dose equivalent / mSv

400 Al-2210
   Polyethylene Hydrogeneded N-absorber Liquid hydrogene

80

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0

0

Sphere thickness / g cm-2

25

50

75

100

Sphere thickness / g cm-2(b) Worst Case SPE at the Moon (left) and Mars (right)
Fig.5.10. Set of calculations showing dose equivalents for different shielding materials versus
Fig.thickness
5.9bshieldingon the surface of Moon (left) and Mars (right) for GCR (a) and a worst-case SPE(4x the fluence of the SPE on Sept. 1989) (b) (Wilson et al., 2001)(258) Much of the protection inside a spacecraft is provided by structural elements and theequipment present in it. For the structure of the spacecraft, a compromise between shielding
efficiency and mechanical stability needs to be chosen, with multifunctional materials needed
to optimize the process. For a shelter inside the spacecraft there are not such restrictions – if
the material is acceptable for space application – and the efficiency per mass is the only
important endpoint. Some recent studies were performed for different shielding materials asshown in Fig 5.11 for vertical incidence (Zeitlin et al., 2006). The effect of the incidence
angle of the particles in producing secondary neutrons is complex and exhibits a strong
interaction with the type of the shielding material. Such studies of course need to beextended.

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Fraction of dose reduction by 1 g cm-2 shielding material

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Fig 5.11. Fraction of dose reduction in a body by a 1 g cm-2 thick shielding for different shielding
materials
and incident Fe particles of 1067 MeV/u. (Zeitlin et al., 2006)
Fig. 5.10(259) Since the earliest attempts at in situ space radiation dosimetry, it has been known
that - even for the most simple transport problems - satisfactory agreement between
measurements and calculations would not be attainable unless the detailed thickness
distribution around the point of interest were known, especially if areas of thinner shield were
present. Therefore estimates of radiation exposures for ‘homogeneous’ ‘isotropic’ shields ofan ‘average’ thickness can only serve for qualitative comparison of different configurations.
For accurate quantitative assessments of radiation exposures, the knowledge of the
distribution of the surrounding shield matter as a function of representative shield thickness isessential.
(260) Shielding to galactic cosmic radiation is generally limited. Nevertheless, with theselection of optimized shield material and an optimal inclusion of consumables in the shielddesign, a significant dose reduction of about 30 % can be achieved at solar minimum and to alesser extent at solar maximum. For SPE’s the reduction is highly dependent on the initial
proton spectrum; however shielding can reduce effective doses by factors of 2 to more than
10. As a first step definition, procurement and characterisation of candidate flexible materials– to be used in future manned missions in LEO and beyond, for inhabited structures has to be
done. Computer codes are the tool to make the characterisation of such materials. The next
step is the improvement and validation of the models and tools for shielding analysis, bycomparison with measurements from accelerator shielding studies and with flightmeasurements, correlation and tuning of models, with the objective of reducing the overall
uncertainty.
5.6

Lunar and Mars Surface(261) There are two effects strongly influencing the radiation environment on planetary or
lunar surfaces compared to the GCR in free space. Because of the shielding of the ground, thecosmic radiation is incident on the surface only in 2-geometry. In addition, from the surfaceof Mars or the Earth’s Moon, albedo radiation occurs. Photons, neutrons or secondary100

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charged particles produced by neutrons will occur and will be dependent on the soil andatmospheric (on Mars) atomic composition including the presence of CO 2 or water frost andhigher neutron fluence rate from lunar or Mars regolith (Clowdsley et al., 2000). Neutrons
may be divided into a forward component produced by GCR interactions with the atmosphereand albedo components on planetary surfaces such as Mars. Albedo neutrons may be
produced as deep as 1 meter into the soil and their flux will be influenced by the soil
composition and seasonal variations in temperature as illustrated in Figure 5.12. Large dust
storms on Mars could lead to additional scattering of neutrons and charged particles (Wilson
et al., 1995a).

Annual spectral neutron fluence / (cm2 MeV)-1

109
108

107
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105
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103

102
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0

10-2

10-1

100

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102

103

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Neutron energy / MeV

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5.11
Fig. Fig.
5.12
Energy distribution of neutron fluence on the Mars surface calculated with HZETRN
showing the annual contributions from the forward component produced by GCR in the Mars
atmosphere and the albedo component that are dependent on the composition of the Mars surface(Wilson et al., 2004).

6.

RADIATION FIELDS AND DOSES IN THE HUMAN BODY(262) The radiation fields inside astronauts differ from those outside because of atomic
and nuclear interactions in the human body. The analysis of particle transport inside the bodyis indispensable for the estimation of doses in astronauts and risks of both stochastic anddeterministic effects due to cosmic radiation exposures. Various simulation codes (see 5.3)
and computational phantoms, which represent the anatomy of human body or parts thereof,
have been employed for this analysis. In radiological protection, the mean absorbed dose inan organ or tissue, DT, is the basic quantity for a specification of doses in humans (seeChapter 3). In addition, appropriate weighting factors need to be applied to DT for theassessment of risk of stochastic or deterministic detriments due to radiation exposure.
(263) Generally, two different procedures may be applied for the assessment of doses in101

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the human body, either by calculations or by measurements combined with calculations.
Radiation field parameters, e. g. particle fluence, particle spectra and LET-distributions,outside or within a spacecraft may be determined either by measurements or calculations andthen doses in organs and tissues of the human body may be calculated using particle transport
codes. There are two possibilities in performing this task. One may either assess the radiation
field parameters (e.g. energy distribution of fluence, D(L)-distributions etc.) (Section 5.3)
near to an astronaut and then apply fluence-to-dose conversion coefficients for all types ofparticles involved for the assessment of organ doses (see Sect. 6.2) or one can generally
calculate organ doses in a body using the radiation field data outside of the spacecraft and acode which combines radiation transport in the spacecraft and in the human body (see Sect.
6.3).
(264) Alternatively, absorbed dose or dose equivalent may be measured near to the bodyof the person of interest and these values may be directly correlated to doses in the humanbody. This is the usual procedure performed in individual dosimetry on the Earth, where thereading of an individual dosemeter for strongly-penetrating radiation is taken as a value ofeffective dose sufficiently precise for the purpose of usual radiological protection. In space,however, this method is a difficult task because of the very complex radiation field, which
also shows variations with time and position within a spacecraft. As shown in Chapter 4, nosingle device will probably be able to fulfil this task, and a set of different detectors may benecessary for the assessment of dose equivalent in an organ or tissue or effective dose
equivalent. The position and orientation of a person within the spacecraft can introduce
variations in organ doses due to the anisotropic spacecraft shielding distributions, which canbe important for solar protons and trapped radiation (Wilson et al., 1995c). In any case,particle transport calculations need to be used for testing if a system is appropriate for theforeseen task.
6.1

Phantoms(265) The first computational phantom was developed at the Oak Ridge National
Laboratory (Snyder et al., 1969) for the Medical Internal Radiation Dose (MIRD) Committeeof the Society of Nuclear Medicine. The MIRD phantom designed as a hermaphrodite
including organs and tissues of both sexes has been widely used in varieties of the radiation
protection researches, in combination with various Monte Carlo codes. On the other hand, theComputerized Anatomical Man (CAM) (Billings and Yucker, 1973) and Computerized
Anatomical Female (CAF) (Yucker and Huston, 1990) phantoms were developed in 1973 and1990, respectively. They have a long history in space radiation research at NASA, in
combination with the transport code HZETRN. These phantoms are based upon mathematicalexpressions representing planes, and cylindrical, conical, elliptical and spherical surfaces that
describe the shape and position of idealized body organs.
(266) As an extension and improvement to these earlier models, various groups havedeveloped a new type of anatomical phantom during the last two decades, called“tomographic” or “voxel” phantom. Voxel phantoms are anatomical models based oncomputed tomography, magnetic resonance, or other images obtained from high-resolutionscans of a single individual and, thus, offer a more realistic replication of human anatomy.
They consist of a large number of volume elements (voxels) and are the most detailed
representation of human anatomy at the present time. However, being derived from a specificindividual, these models do not represent the average Caucasian man or woman as defined by
Publication 23 (ICRP, 1975) and Publication 89 (ICRP, 2002). To avoid this inconsistency,
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the Commission introduced reference voxel phantoms representing the adult Reference Maleand Reference Female defined in Publication 110 (ICRP, 2009), which were constructedbased on medical image data of real persons, but their anatomical parameters were modified
to be consistent with those given in Publication 89. These phantoms are used by theCommission in establishing radiation protection guidance and reference data, e.g. conversion
coefficients for dosimetric quantities. NASA has used the voxel approach based on the
MAX/FAX voxel model in a ray tracing approach appropriate for the HZETRN code (Slabaet al. 2010, Kim et al., 2010b)(267) One limitation of the phantoms is that their resolutions are not high enough to
reproduce the thin structure of a tissue or organ located at or near to the surface of human
body, e.g. skin and lens of the eye. This causes both overestimation and underestimation ofdoses in such tissue and organ for the irradiation by low-energy particles such as trapped
protons and electrons. Thus, special procedures are required to precisely calculate the dose insuch tissues or organs, using the phantoms. A more detailed description on this issue is given
in Publication 110 (ICRP, 2009).
(268) For realization of anthropomorphic phantoms, several materials such as water andtissue-equivalent plastics are used on ground. On the other hand, only solid plastic phantoms
can be launched to space for practical reasons. The RANDO® phantoms of head and upper
torso had been mounted on the Space Shuttle (Konradi et al., 1992, Yasuda et al., 2000,
Badhwar et al., 2002) and the ISS (Cucinotta et al., 2008). The other RANDO®phantom had
been exposed outside the ISS as a part of the MATROSHKA project (Reitz et al., 2009). A
spherical phantom composed of tissue-equivalent plastic has also been mounted on the ISS aspart of the MATROSHKA-R project (Shurshakov et al., 2004). A number of passive andactive detectors were inserted in or attached on the phantoms. The data obtained from thedetectors are useful in validating the accuracy of particle transport simulations performed
using the computational phantoms.
6.2

Dose conversion coefficients

Mean absorbed dose in organs and tissues(269) For a given organ T and radiation type R, the mean absorbed dose in the organ, DT,R,
can be obtained folding the energy distribution of the fluence of particles incident on thehuman body with the fluence-to-absorbed dose conversion coefficients for that organ,
dT,R(E). It is:

d R
(6.1)
DT, R   d T, R ( E )
dE ,
dE
0
where ΦR is the fluence of particles of type R incident on the body. Because conversion
coefficients, dT,R, are mainly available for a homogeneous exposure of the human body, only,
the application of this equation assumes always a uniform exposure of the body. In cases
where this assumption is not approximately satisfied, further considerations are needed forthe application of this approach.
(270) For assessing organ doses it is necessary to have conversion coefficients for allorgans and tissues of the human body, for all particles and energies of interest and for the realgeometry of irradiation.
(271) For the calculation of conversion coefficients, an exposure of a mathematical
anthropomorphic phantom is simulated for the incidence of monoenergetic particles
according to simple geometries, mostly homogeneous frontal incidence (AP), incidence from103

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the right or left side (RLAT, LLAT), from the back (PA) or rotational (ROT) and isotropic(ISO) exposure. The isotropic irradiation is usually assumed to appropriately describe theexposure of astronauts to cosmic radiation, mainly due to the isotropic fluence rate of the
GCR and the movement of the astronauts in the spacecraft. Nevertheless, this assumption
may not always represent the situation well (Wilson et al., 1995c).
(272) The absorbed dose in the various organs and tissues of the human body are
estimated from the energies deposited in the regions assigned to each organ divided by theirmasses. In the case of the voxel phantoms the mean absorbed doses in the organs are
estimated from the energies deposited in the voxels assigned to each organ divided by theorgan mass. This method has been applied in most organs, including skin, for the calculationsof the conversion coefficients adopted by the Commission. Exceptions are the red bonemarrow and bone surface (endosteum), which are tissues not explicitly deﬁned in thereference phantoms. According to Schlattl et al. (Schlatt et al., 2007), the mean absorbed dosein red bone marrow, DRBM, and in endosteum, DEndosteum, are determined respectively bym RBM,i(6.2)
DRBM  
Dspongiosa,ii m RBMandmEndosteum,iDEndosteum  Dspongiosa,i(6.3)
i m Endosteum
where mRBM,i is the mass of RBM in i-th spongiosa region, mRBM the total mass of RBM,
Dspongiosa,i the dose of i-th spongiosa region, mEndosteum,i the mass of endosteum in i-thspongiosa region and mEndosteum the total mass of endosteum.
(273) As an example, conversion coefficients for red bone marrow and gonads,
respectively, published by the Commission for isotropic irradiation of the reference adultmale and female phantoms are shown in Fig. 6.1 as a function of neutron energy (ICRP,
2012).

Fig. 6.1. Fluence to mean absorbed dose conversion coefficients for red bone marrow (left) andgonads (right) as a function of neutron energy for isotropic irradiation of the adult male and female
reference phantoms (ICRP, 2012).

(274) Figure 6.2 shows similar conversion coefficients for red bone marrow and skin,respectively, as a function of energy for protons (ICRP, 2012). It should be noted that thegender dependence of the organ doses are significant only for few organs and varies with thetype and energy of the radiation involved.

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Fig. 6.2. Fluence to mean absorbed dose conversion coefficients for red bone marrow (left) and skin(right) as a function of proton energy for isotropic irradiation of the adult male and female reference
phantoms (ICRP, 2012).

(275) The fluence to mean absorbed dose conversion coefficients for organs and tissues ofthe body have been systematically calculated for heavy ions with atomic numbers up to 28
and energies from 1 MeV/u to 100 GeV/u using the PHITS code coupled to the reference
voxel phantoms (Sato et al., 2010), following the instruction given in Publication 103 (ICRP,
2007). A full set of data for male and female and isotropic exposure of the body is given in
the Annex of this report.
(276) As an example, the data for red bone marrow (RBM), breast, stomach and skin areplotted in Figures 6.3 for isotropic (ISO) irradiation of the reference adult male phantom with
4
He and 28Si ions, respectively.

Fig. 6.3. Fluence to mean absorbed dose conversion coefficients for various tissues as a function ofparticle energy for isotropic irradiation of the reference adult male phantom by 4He ions (left) and 28Si
(right).

(277) It can be seen from figure 6.3 that the dose conversion coefficients for the organs arevery different for the energies below about 200 MeV, while they are very similar for highenergies. At low energies, the incident particles have short ranges in tissue and will generally
stop in an organ or tissue near to the surface (i.e. skin). At high energies, on the other hand,
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the incident particles have very long ranges and generally penetrate the human body without
forming the Bragg peak. Thus, the doses are more uniformly distributed inside the humanbody in comparison to low-energy particle irradiations.

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(278) While fluence to mean absorbed dose conversion coefficients for organs and tissues,dT,R, are the basis for dose assessment in the human body, in mixed radiation fields withradiations of very different radiation quality fluence to dose equivalent conversion
coefficients, hT,Q,R, for organs and tissues are often more appropriate for radiation protection
applications and risk assessments in space environment. Most space organizations (e.g.
NASA, ESA, etc.) have adopted these quantities and corresponding conversion coefficients
since the late 1990s (NCRP, 2000).
(279) The calculation of the conversion coefficients for mean dose equivalents in organs
and tissues and effective dose equivalent, are more complex than those for the absorbed
doses, because the doses at the point of interest must be weighted by the quality factor as afunction of LET. In this case, the charge and energy of ionizing particles depositing theenergy at that point have to be determined. If kerma factors are used for determining themean absorbed dose in tissues and organs (e.g. for neutrons below about 20 MeV) this does
not allow the evaluation of a Q-value unless one includes further corrections.
(280) The dose equivalent in an organ or tissue T, HT,Q, is calculated by:

3581

Organ and effective dose equivalent

H T, Q    hT, Q, R ( E )
R E

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d E
d E
dE    QT, R ( E )d T.R ( E )
dE
dE
dE
R E

(6.4)

with the mean quality factor QT,R based on Q(L) as given in eq. (3.10).
(281) The mean quality factors, QT,R, and the fluence to organ dose equivalent conversion
coefficients, hT,Q,R for organs and tissues have been systematically calculated for heavy ionswith atomic numbers up to 28 and energies from 1 MeV/u to 100 GeV/u using the PHITS
code coupled to the reference voxel phantoms (Sato et al., 2010). Data of mean quality
factors for organs and tissues and isotropic exposure of the body are also given in the Annex
to this report.
(282) The organ dose equivalent conversion coefficients obtained by PHITS for red bonemarrow, breast, gonads (testes and ovaries, respectively) and skin of the adult male andfemale reference phantoms are depicted in Fig. 6.4 and 6.5 for ISO irradiation by 4He and56
Fe, respectively.

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Fig, 6.4. Fluence to organ dose equivalent conversion coefficients for various tissues as a functionof the particle energy for 4He ions and isotropic irradiation of the adult male (left) and female (right)
reference phantom.

Fig. 6.5. Fluence to organ dose equivalent conversion coefficients for various tissues as a functionof the particle energy for 56Fe ions and isotropic irradiation of the adult male (left) and female (right)
reference phantom.

(283) As far as fluence-to-effective dose equivalent conversion coefficients are concerned,
the data for neutrons are very similar to those for effective dose. Larger differences between
conversion coefficients for effective dose and effective dose equivalent exist for low energy
protons, where the value of the mean quality factor is much higher than the value of 2 for theradiation weighting factor. In high-energy proton fields, however, this difference is not very
important because of the small contribution of low-energy protons to effective dose andeffective dose equivalent. Fig. 6.6 presents some data for several heavy ions.

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Fig. 6.6. Fluence to effective dose equivalent conversion coefficients for several particles as afunction of the particle energy for isotropic irradiation of adult male reference phantom.

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Fig. 6.7. Mean quality factors, QT,ISO, based on Q(L) as defined in Publication 103, of some tissues
as a function of particle energy for isotropic exposure of the adult female reference phantom by (a) p,(b) 4He, (c) 12C and (d) 56Fe.

(284) The ratio of the mean dose equivalent in an organ to the mean absorbed dose in that108

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organ gives the mean quality factor for that organ. As an example, Figures 6.7 a-d shows themean quality factors for red bone marrow, breast, stomach and skin for exposure of the adultfemale reference phantom by protons, 4He-, 12C- and 56Fe-ions.
(285) As can be seen in Fig. 6.7, for isotropic exposure to a specific ion type thedifferences in QT of the different organs and tissues are relatively small. Therefore, a humanbody averaged quality factor (performed by weighting the organs and tissues (see eq. (3.12))
using the tissue weighting factors given by the Commission (ICRP, 2007)) represents theradiation quality well in isotropic exposure situations.

(a)(b)
Fig. 6.8.
Phantom averaged quality factor, QE,ISO, as a function of neutron energy (a) and protonenergy (b) for isotropic (ISO) exposure of the adult male reference phantom. The wR-functions are
additionally shown (dotted line).

(286) While for AP radiation incidence body averaged quality factors for neutrons andprotons are shown in Figs. 3.3 and 3.4, for data for isotropic exposure are given in the Annex
and presented in Fig. 6.8a,b. In Fig. 6.9a, b similar data are shown for various heavy ions.

Fig. 6.9. Phantom averaged quality factor, QE,ISO, as function of particle energy for various particles
and isotropic exposure of the adult male reference phantom.

(287) Mean quality factors for organs and tissues, QT,NASA, based on the Q-function as
proposed by NASA for solid cancer (see Fig. 3.14), were also calculated using the PHITS
code coupled to the reference voxel phantoms (Sato et al., 2012). As an example, figures 6.10
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a-d show QT,NASA of the red bone marrow, breast, stomach and skin for isotropic exposure byprotons, 4He, 12C and 56Fe ions. The values of red bone marrow were calculated using theNASA quality factor for leukaemia which is 1/4 of that for solid cancer.
(288) For proton and light ions, the values of QT,NASA are generally larger than thecorresponding data based on the Q(L) function given in eq. (3.9) ICRP (Fig. 6.7), except for
red bone marrow. For heavier ions, however, the values of QT,NASA are generally smaller thanthe corresponding values based on the ICRP function especially for very low and very highparticle energies. The smaller QT,NASA observed at low energies is attributed to the strong
decrease of QT,NASA with increasing L in the high-LET region, while for high particle energies
the consideration of the track structure in the NASA concept is important.

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Fig. 6.10. Mean quality factors, QT,NASA , based on the Q-function proposed by NASA, of someorgans as a function of particle energy for isotropic exposure of the adult female reference phantomby (a) protons, (b) 4He, (c) 12C and (d) 56Fe.

(289) Figure 6.11 shows human body averaged quality factors based on QT,NASA for
isotropic exposure of the adult female reference phantom by various particles. The tissue
weighting factor, wT, as defined in Publication 103 (ICRP, 2007) were adopted in thecalculation.

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Fig. 6.11
Phantom averaged quality factor, QE,ISO,NASA, as function of particle energy for protons(a), neutrons (b) and various other ions (c) and isotropic exposure the adult male reference phantom.

6.3

Calculation of organ doses of astronauts within spacecraft(290) Generally, organ doses in a body may be calculated using the radiation fieldparameters outside the spacecraft and a code which combines radiation transport in thespacecraft and in the human body. In principle, this procedure takes account of all
inhomogeneities of the radiation field inside the spacecraft due to the variations in thespacecraft wall and the distribution of the material inside the spacecraft. The approach has
been realized by NASA using the very fast radiation transport code HZETRN together withvarious human phantoms (see e.g. Wilson, et al., 1995c, Badhwar et al., 2002, Cucinotta et al.,2008). The external radiation field parameters to be known include the energy and directional
distribution of the fluence of all types of radiation involved. Also the time dependence ofsome contributions needs to be known. This approach can be applied to the field for EVA andfor astronauts in a habitat on the moon or planet.
(291) For checking this method, phantom torsos comprised of realistic distributions ofhuman tissue equivalent materials have been flown on several space shuttle missions. Organdose equivalents have been estimated by using a combined TLD and PNTD (CR-39) detector
methodology (Badhwar et al., 2002; Yasuda et al., 2000). Table 6.1 shows a comparison ofdata calculated using the HZETRN/QMSFRG model (Cucinotta et al., 2008) to those from111

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measurements of Yasuda et al. (2000) on space shuttle mission STS-91, which flew in a 51.6
inclination orbit to the Mir station a similar orbit as flown by ISS. The corresponding data
calculated by PHITS coupled with the dose conversion coefficients for isotropic irradiation
are also given in the table (Sato et al., 2011).The comparison shows excellent agreement
between measured and calculated data. The NASA phantom torso experiment that was flown
on STS-91 (Badhwar et al., 2002), was re-flown on ISS Increment 2 in 2001. This experiment
included several small active silicon detectors located at critical organ positions in the torsothat provide time dependent dose data. The correlation of the time dependent data to the ISS
trajectory allows for separation of the individual contributions from trapped protons and GCR
to organ doses. Table 6.2 shows comparison of the HZETRN/QMSFRG results (without
scaling) to the measurements indicating good agreement. The results show that the ratio of
the GCR to trapped proton absorbed dose is about 2:1. Mean quality factors without tissue
shielding for GCR (~3.5) are more than twice as high as that for the trapped protons (~1.5).
These results support the assumption that organ dose equivalents for ISS missions and many
space shuttle missions are predominantly from GCR.

3708
3709
3710
3711

Table 6.1. Comparison of measured organ dose equivalent for STS-91 mission using a combined
PNTD/TLD method and data calculated using the HZETRN/QMSFRG model with randomorientation in the spacecraft (Yasuda et al., 2000), as well as using PHITS coupled with the doseconversion coefficients(DCC) for isotropic irradiation (Sato et al., 2011).
TissueOrgan dose equivalent / mSv
Measured
HZETRN/Diff.
PHITS/Diff.
QMSFRG%
DCC%
Skin
4.5 +0.05
4.7
4.4
5.3
18.5
Thyroid
4.0 +0.21
4.0
0
4.2
4.9
Bone surface
5.2 +0.22
4.0
-23.1
4.3
-17.8
Esophagus
3.4 +0.49
3.7
8.8
3.6
5.4
Lung
4.4 +0.76
3.8
-13.6
3.9
-12.3
Stomach
4.3 +0.94
3.6
-16.3
3.5
-17.5
Liver
4.0 +0.51
3.7
-7.5
3.6
-10.7
Bone marrow
3.4 +0.40
3.9
14.7
3.7
9.5
Colon
3.6 +0.42
3.9
8.3
3.7
1.9
Bladder
3.6 +0.24
3.5
-2.8
3.5
-2.3
Gonad
4.7 +0.71
3.9
-17.0
4.2
-10.3
Breast4.5 +0.11
4.5
0
5.2
16.2
Remainder
4.0 +0.57
4.0
0
3.7
-6.5
Effective dose
equivalent
4.1 +0.22
3.9
4.9
3.9
4.9

3712
3713
3714
3715
3716
3717

Table 6.2. Comparison of the organ absorbed dose rate measured by the ISS Increment-2 Phantom
Torso experiment (July-August, 2001) with predictions obtained using the HZETRN/QMSFRG
model at a fixed position in the spacecraft (Badhwar et al., 2002).

Organ

Brain

Absorbed dose rate Absorbed dose rate
Total
trapped radiationfrom GCR
absorbed dose rate
mGy/d
mGy/d
mGy/d
Exp.
Model
Exp.
Model
Exp.
Model
0.051
0.066
0.076
0.077
0.127
0.143

112

Difference
(%)
13.3

DRAFT REPORT FOR CONSULTATION
ThyroidHeart
Stomach
Colon
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728

0.062
0.054
0.050
0.055

0.072
0.061
0.057
0.056

0.074
0.075
0.076
0.073

0.077
0.076
0.077
0.076

0.136
0.129
0.126
0.128

0.148
0.137
0.133
0.131

9.4
6.7
5.5
2.5

(292) The doses received in interplanetary missions have been evaluated by the same
approach by a number of authors (i.e. Badhwar et al., 1994; Cucinotta and Durante, 2006a,
Hoff et al., 2004, Zapp et al., 2002, Ballarini et al., 2006, Trovati et al., 2006). The FLUKA
code associated with a Golem voxel phantom (Zankl et al., 2001) was used for an estimate ofthe doses inside a capsule-like enclosure with variable Al-wall thickness (Ferrari, 2007). It
was supposed that particles of GCR impinge uniformly and isotropically on the spacecraft.
As an example, Figure 6.12 shows calculated results in terms of absorbed dose rate to redbone marrow (RBM) as a function of the thickness of the Al wall. The contribution of the
primary particles to the total dose rates is also shown in Figure 6.12.
0.45



DRBM / mGy d-1

0.40
0.35

0.30
0.25
0.20
0.15
0.10

0.05
0.00
0
5
10
-2
Al thickness / g cm

3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744

Fig.6.12. Absorbed dose rate to red bone marrow (RBM) of a voxel phantom exposed to galactic
cosmic Fig.
radiation
inside a capsule as a function of the Al wall thickness of the capsule (Ferrari, 2007).
6.10(293) The calculated absorbed dose rate behind 1 g cm-2 of Al resulted in 0.378 mGy/d,with 59% due to protons, 21% to alpha particles, 10% to ions of 2 < Z ≤ 8, 5% to ions of
8 < Z ≤ 14 and 5% to ions of Z > 14. The dose rate contributions of the various ion groups
include those of primary ions and of all products generated in their interactions. The dose rate
contribution of the uncollided particles was 0.206 mGy/d.
(294) Examples of direct evaluation of the organ dose equivalent rates from externalradiation fluence rates of GCR without use of conversion coefficients are shown in Fig. 6.13.
Similar to simulations already described above (see Fig. 6.12) the figure shows the dose
equivalent rate to RBM as a function of the Al wall thickness of a capsule (Ferrari, 2007). It
should be noted that for these data the tissue weighting factors recommended in the
Publication 60 (ICRP, 1991) were applied.

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DRAFT REPORT FOR CONSULTATION

Dose equivalent rate / mSv d-1

3745
1.4
1.2
1.0

0.8
0.6
0.4
0.2

0.0
Al thickness / g cm-2

3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774

Fig 6.13. Dose equivalent rate to the RBM of a voxel phantom inside a capsule exposed to galactic
cosmic radiation as a function of the Al wall thickness of the capsule (data from Ferrari, 2007).
Fig. 6.11(295) The calculated RBM dose equivalent rate behind 1 g cm-2 of Al is 1.26 mSv/d,
where 31% are due to protons, 11% to alpha particles, 13% to ions of 2 < Z ≤ 8, 16% to ionsof 8 < Z ≤ 14 , 29% to ions of Z > 14. The contributions of the various ion groups include theprimary ions contributions and those of all products generated in their interactions. The
contribution of the uncollided particles was 0.72 mSv/d.
(296) Several other authors used the method described above in order to determine theorgan dose equivalent and effective dose equivalent received by the astronauts, especially forstudying the shielding effect of the wall thickness of the capsule. Slaba et al. (Slaba et al.,2010) computed the protection quantities under both a galactic cosmic radiation and solar
particle event environment. The spherical shell of aluminum was supposed isotropically
irradiated and various computational models (CAM, CAF, MAX, FAX) have been used.
Ballarini et al. (2006) and Trovati et al. (2006) calculated the GCR and SPE organ doses indeep space with different shielding by Monte Carlo simulations using the FLUKA code
coupled to a mathematical model and a voxel phantom.
(297) Furthermore, it is of interest to which extent the values of dose equivalent in theseradiation fields depend on the different concepts of the quality factor. As function of Z of the
primary incident particle with an energy distribution as given in the GCR field, Fig. 6.14 shows
a comparison of body-averaged mean quality factors using the Q(L) relationship and the recent
NASA approach to quality factors based on particle track structure concepts and using different
quality factor values for solid cancers and leukaemia. The calculations are made using the
HZETRN code for solar minimum in the orbit of the International Space Station (ISS). Different
calculations were carried out applying either a thin (5 g/cm2) or a thick (20 g/cm2) aluminum
shielding. Differences between the different approaches occur mainly for low- and high-Z
particles.

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DRAFT REPORT FOR CONSULTATION

Q(L) (A)QNASA, solid (A)Q(L)

Body-averaged Q

QNASA, leukaemia (A)Q(L) (B)QNASA, solid (B)

QNASA, leukaemia (B)

QNASA, solid cancer

QNASA, leukaemia

3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804

Z
Fig. 6.18

Figure 6.14. Comparison of body-averaged quality factor values as a function of primary incident
particle of charge Z calculated by applying either the ICRP Q(L) function or the NASA quality factors
for solid cancers or leukaemia for thin or thick aluminum shielding conditions. (A) 5 g/cm2 Al
shielding; (B) 20 g/cm2 Al shielding.

6.4

Assessment of doses in the body by measurements(298) Specific operational quantities for an assessment of dose in the body of astronauts inspace have never been defined. Some properties of the radiation field, however, may provide
some help in the determination of effective dose equivalents of astronauts. Firstly, there is amajor component of very high-energy particles with long ranges in tissue in the field whichstrongly contribute to doses in the body. Secondly, the radiation incidence on the body may
be nearly isotropic considering the situation that the astronauts are usually moving aroundand are not fixed in a special position for long times. Therefore, isotropic exposure ofastronauts has been assumed in calculations resulting in a relatively homogeneous dose
distribution within the body from GCR exposure (see Fig. 6.12 and 6.13). This, however, is
not the case for low-penetrating radiation which mainly contributes to doses of the skin andother tissues near to the surface.
(299) Any dose-measuring system, therefore, must have the ability to discriminate
between strongly- and low-penetrating radiations. In addition, information about the
distribution of absorbed dose in tissue in terms of lineal energy L, DL, is necessary for theassessment of equivalent dose in the body.
(300) Measurement of dose distributions and organ doses in a human phantom in spacehave also be performed by the MATROSHKA collaboration (Reitz and Berger, 2005; Reitz
et al., 2009) and exploited by members of the HAMLET collaboration (see www.fp7hamlet.eu). A tissue-equivalent anthropomorphic phantom, called MATROSHKA, has beenequipped with hundreds of dosemeters of different types, mostly TLD and NTD - andexposed in space during various ISS missions.
115

DRAFT REPORT FOR CONSULTATION
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814

(301) The MATROSHKA experiments provide detailed depth dose distributions in ahuman phantom exposed outside the ISS (MTR-1 mission) and in two positions inside theISS at different shielding locations (MTR-2A, MTR-2B missions). Figure 6.15a shows themeasured dose rate distribution in the MATROSHKA phantom for the MTR-1 mission basedon TLD readings at 1598 locations inside the phantom. For measurements with the phantom
outside the ISS, the absorbed dose rates range from 0.1 mGy/d to 0.5 mGy/d, with the highest
dose at the phantom surface. For other missions inside the ISS due to the spacecraft shielding
the absorbed dose rates are mostly restricted to a range from 0.13 mGy/d to 0.23 mGy/d.

MTR-1

MTR-2A

Absorbed dose ratein mGy/d0.5

Absorbed dose ratein mGy/d

0.4

0.3
0.2
0.1

Fig. 6.12a

3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833

a)

b)
Fig. 6.12b

Fig. 15. (a) Measured absorbed dose rate distribution in the MATROSHKA phantom for the
MTR-1 mission outside of the ISS based on TLD readings (Reitz, 2012).
(b) Absorbed dose rate distribution in the MATROSHKA phantom for the MTR-A2 mission inside
the ISS obtained by interpolation of point doses over the whole phantom volume (Reitz, 2012).

(302) Computer tomography scans of the MATROSHKA phantom are taken in order tobuild up a voxel model called NUNDO (Numerical Rando). A computer program allows
calculation of dose distributions by interpolation of point doses over the whole phantom
volume (see Fig. 6.15b). For total absorbed dose and dose equivalent rate distributions andhence an assessment of mean absorbed dose rates and dose equivalent rates in organs andtissues, data measured by TLD and PNTD have been combined. The dose equivalent rate wascalculated using quality factors as defined in ICRP Report 60 (ICRP, 1991).
(303) The high dose gradient near to the skin for the MTR-1 missions is due to the highcontribution of electrons and protons at the South Atlantic Anomaly. Inside the ISS thiscontribution is strongly reduced due to the shielding by the spacecraft (see Fig. 6.16 and6.17). The dose rates in the deeper lying organs are nearly constant due to the high energies
and nearly isotropic fluence distribution of the GCR. For astronauts moving within thespacecraft, this is even more the case.

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DRAFT REPORT FOR CONSULTATION

Absorbed dose rate (mGy/d)

1,4
MTR-1
MTR-2A
MTR-2B

1,2
0,6

0,4

0,2

3834
3835
3836
3837

S
Ey kin
e
le
ns
Br
ea
s
Sa
Te t
liv
a r s te
s
y
gl
an
d
Th s
yr
oi
d
Br
ai
n
Bo
ne
R
ed
s
C
bo
ne olom n
Es arro
op w
h
R agu
em
s
ai
nd
er
Sm
al Liv
li
nt er
es
t
St ine
om
ac
h
Lu
ng
Bl s
ad
de
Ki r
dn
ey

0,0

Fig. 6.16
Mean absorbed dose rates in organs and tissues of the MATROSHKA phantom during
different space missions at the ISS determined from measurements using TLD and PNTD (Reitz,2012).
3,0

Dose equivalent rate (mSv/d)

Fig. 6.21

MTR-1
MTR-2A
MTR-2B
2,5
1,5

1,0

0,5

3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850

S
E y k in
e
le
ns
Br
ea
s
Sa
Te t
liv
ar ste
s
y
gl
an
ds
Th
yr
oi
d
Br
ai
n
Bo
ne
R
ed
s
C
bo
ne olom n
Es arro
op w
h
R agu
em
s
ai
nd
er
Sm
al Liv
li
nt er
es
t
St ine
om
ac
h
Lu
ng
Bl s
ad
de
Ki r
dn
ey

0,0

Fig. 6.17. Mean dose equivalent rates in organs and tissues of the MATROSHKA phantom during
different space missions at the ISS determined from measurements using TLD and PNTD (Reitz,2012).
Fig. 6.22(304) The measured organ absorbed dose data were compared with corresponding values
obtained from dose conversion coefficients multiplied with cosmic-radiation fluxes in thespacecraft calculated by PHITS using a simplified geometry of the ISS (Sato et al 2011). The
agreement was found quite satisfactory in spite of some discrepancies observed for someorgans, taking account of the various approximations introduced, in primis the hypothesis of
isotropic irradiation.
(305) Similar data have been calculated for comparison with organ absorbed doses
measured by the MATROSHKA experiment outside the ISS. As shown in Table 6.3 an

117

DRAFT REPORT FOR CONSULTATION
acceptable agreement has been achieved.
Table 6.3. Organ absorbed dose rates measured by the MATROSHKA experiment outside ISS (Reitz
et al., 2009) in comparison with corresponding calculated dose rates obtained from PHITS
simulations (Sato et al., 2011).
Organ/Tissue

Measured absorbed dose rate
mGy/d
0.944
0.33
0.39
0.26
0.24
0.242

Skin
Salivary glands
BreastLung
Oesophagus
Stomach

0.35
0.30
0.25
0.20
0.15
0.10

TestesBladder

Salivary glands

Liver

Brain

Bone

Colon

Oesophagus

Thyroid

StomachBreast

Skin

0.00

Lung

0.05
Red bone marrow

3868
3869
3870
3871

Calculated absorbed dose rate
mGy/d
1.814
0.435
0.690
0.279
0.250
0.245

(306) The agreement is seen to be very good for the interior organs such as lung,oesophagus and stomach. The calculation, however, substantially overestimates the measured
absorbed dose rates for the organs located near to the surface of the body, especially for theskin. That is probably due to the effect of a high yield of low-energy trapped protons andelectrons encountered and also to some differences between phantoms and geometries of
their surrounding environment employed in the calculation and experiment.
(307) The accuracy of heavy ion transport codes was discussed in Section 5.3.1. With
respect to the different anthropomorphic voxel models used the differences in the values ofabsorbed dose and dose equivalent of single organs and tissues calculated using the NUNDO
model (MATROSHKA) or the ICRP reference voxel phantom are quite small as shown in
Fig. 6.18 (Matthiä, 2012).

dDT/dt /mGy d-1, dHT,Q/dt /mSv d-1

3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867

Remainder

3851
3852
3853
3854
3855

Fig. 6.18. Mean absorbed dose rate and dose equivalent rate in various organs and tissues
calculated using the GEANT4 code and the NUNDO model and the ICRP reference phantom forgalactic cosmic radiation (Matthä, 2012).

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DRAFT REPORT FOR CONSULTATION
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895

6. 5

Biodosimetric measurements(308) Biodosimetric measurements offer an alternative to the measurement of individual
doses external to the body of an astronaut for the assessment of effective dose equivalent,because of the very complex radiation field in the spacecraft which in addition is varying in
intensity and composition with time. Lymphocytes in the human body are circulating andhence provide a target which is well distributed over the human body. In addition, the RBELET dependence for total chromosomal exchanges during the first cell cycle is similar to the
Q(L) relationship defined by the Commission (see Fig. 3.4) when using the prematurechromosome condensation method (Cucinotta et al., 2008).
(309) The method has already been applied for estimating doses of astronauts in space
shuttle flights (George et al., 2001), at the MIR station (Yang et al., 1997, Fedorenko et al.,2001) and at the ISS (Cucinotta et al., 2008).
(310) In Table 6.4 doses obtained by physical and biological dosimetry for ISS missions
are compared, where the comparison includes biomarker results based on an individual or
population based calibration using gamma radiation (Cucinotta et al., 2008). Mission lengthsof 4 to 7 months occur for the different results described. Biomarker results are given interms of RBE·D (unit: mGy). This RBE-weighted dose value may be compared with valuesof dose equivalent to organs or tissues (here with the dose equivalent of the skin) andeffective dose equivalent obtained from dosemeter readings and applying the Q(L) relation as
given by Publication 103 (ICRP, 2007). The overall agreement between the methods lends
confidence that the complex environment in space has been adequately characterized.

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DRAFT REPORT FOR CONSULTATION
3896
3897
3898
3899

Table 6.4. Data of mission doses of ISS astronauts obtained by biological dosimetry and bymeasurements with individual dosemeters (Cucinotta, 2008). The data of skin dose equivalent andeffective dose equivalent are obtained by calculations adjusted to the individual’s dosemeter readings.
Astronaut

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Mean*

3900
3901
3902
3903
3904

RBE·D
mGy

Individual dosemeter reading

Individual
based calibr.

Population
based calibr.

in mGySkin dose
equivalent(calc.)
mSv

94 ±12127 ±57
78 ±1660 ±2436 ±1559 ±1941 ±1983 ±29113 ±1774 ±32128 ±40134 ±4566 ±21
83 ±27
10 ±24147 ±48
113 ±26
119 ±32
85 ±38128 ±2584 ±41
81 ±1987 ±2054 ±2661 ±21
72 ±2740 ±21130 ±2575 ±2655 ±2671 ±2488 ±2959 ±15125 ±52
15 ±35134 ±66
109 ±34
69 ±23
81 ±32

31
30
33
32
29
32
29
31
40
31
22
23
22
26
30
20
36
30
24
28.9 ±4.9

89.9
86.5
96.4
93.8
85.1
90.8
83.3
88.3
115
88.3
64.5
65.4
64.7
78.0
88.6
56.8
103.0
83.7
70.1
83.8±14.1

Effective dose
equivalent(calc.)
mSv
77.6
73.7
82.1
79.9
72.5
80.0
70.6
74.7
98.6
74.5
54.7
55.7
59.8
66.3
75.2
47.5
86.3
76.9
59.5
71.9 ±12.0• Uncertainties listed are based on the data variation in the column and do not include measurement
uncertainties.

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DRAFT REPORT FOR CONSULTATION
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952

7.

OPERATIONAL RADIATION PROTECTION IN SPACE(311) The guiding principles used for radiation protection on Earth including justification,dose and risk limitation and ALARA are essential also for radiation protection during spacetravel. Operational radiation protection for astronauts in space, however, differs significantly
from those requirements for external radiation exposure on Earth (see for example EC, 2009).
On Earth, doses are generally well below annual limits; if constraints are approached, better
estimates of effective dose are made from the results of measurements of operational
quantities. For astronauts, doses are mainly based on the environmental situation in space,being typically about 1 mSv per day. Radiation protection for missions includes a large rangeof different measures which should all have the aim of reducing the radiation exposure ofastronauts to a level where the health risks are acceptable (NCRP, 1989). In contrast to manyof the other flight risks, effects from radiation exposure can have long latency times, andcancer and other detriments may occur long after a space mission has ended. However, as
noted by the NCRP (NCRP, 1989, 1997) and discussed by others (Schimmerling 2010;
Cucinotta et al., 2011b), the acceptance of radiation risks in spaceflight should consider manyfactors both dependent and independent of other flight risks.
(312) The operational radiation protection for each mission is to assess the radiation
exposure of astronauts in space. This is prospectively performed by calculating organ andtissue doses weighted for radiation quality and, if needed also effective dose equivalentconsidering tissue weighting, for comparison with mission dose or risk limits related tostochastic and tissue reactions. After the mission, all available data should be combined,
including results from measurements of area and individual instruments, to assess the doses
and the probability of a radiation induced event.
(313) There may be defined special dose levels or constraints for short term exposure,annual exposure, and for an astronaut’s career. The dose levels should apply to the assessed
total detriment, to the lens of the eye, and to the skin. The total detriment is related to aprobability of cancer risk. The dose constraints for tissue reactions are to avoid theoccurrence of impairment during or after a mission. The complex nature of the radiation fieldin space requires continuous analysis of the environment by calculation, area monitoring of
the astronauts’ environment, and, where possible, the analysis of the results of active personal
dosemeters, in order to meet action levels and the dose limits.
7.1

Pre-flight mission design(314) The flight mission design needs to be carried out with the aim of reducing radiation
exposures in line with ALARA. The application of ALARA requires that the space radiation
environment is well known – outside and inside a spacecraft. This requires knowledge of theexternal radiation environment with its various components (see Chapter 2), of thespacecraft/habitat construction, and of the results of transport calculations modelling theinternal radiation environment.
(315) The design of the spacecraft/habitat requires the use of radiation transport codes tocompute dose equivalents. As described in Chapter 5 the computer codes may be one- or
three-dimensional, deterministic or based on Monte Carlo (MC) methods. The construction ofa spacecraft/habitat should include areas where the dose rates are lower than elsewhere in thespacecraft. There should be area monitors with visual displays of dose rates.
(316) To reduce uncertainties (see 7.5) further improvements are needed in the models of121

DRAFT REPORT FOR CONSULTATION
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000

the galactic cosmic radiation, the solar energetic particles, and the trapped radiation to allow
the accurate forecasting of the fully integrated model of the radiation environment incident on
the spacecraft/ habitat. Models have been developed for each of the radiation components.
These models suffer several shortcomings: (i) the GCR models inadequately characterize thesolar cycle dependency and the scaling with heliocentric distance; (ii) the SPE models havean incomplete understanding of the acceleration mechanism of the transport through the
heliosphere and a lack of prediction capability; (iii) the radiation belt models no longer reflect
the current state of the Earth’s magnetosphere and lack the ability to properly describe thedynamic behaviour of the trapped particles.
(317) The forecast models require an improved understanding of the physical processes on
the Sun; the transport and acceleration of the solar wind through the heliosphere; theprocesses in the magnetosphere (wave-particle interactions, source and loss processes, andacceleration mechanisms). The space environment is highly variable on very different timescales as a result of the variability of the Sun.
(318) In general all aspects of the space environment are affected, but SPEs and CMEs are
the most dramatic radiation events and may constitute for several missions a serious hazard.
All the radiation components (including GCR and trapped) are also modulated by SPEs
(Forbush decreases in the GCR fluences, for example). An accurate prediction of SPEs and
CMEs would allow for a more effective approach in the shielding strategy. Forecasting
through real time observation and propagation modelling should be improved.
(319) Astronauts are particularly vulnerable during EVAs, when they should be monitoredwith active dosemeters. Real-time space weather predictions and remote satellite and areas
instrumentation will assist in EVA activity. The real-time measurements will provide
guidance, and can suggest changes in mission scheduling to maintain the total risk below
predefined limits.
(320) The development of shielding requirements and strategies is important for theachievement of ALARA. The reduction in exposure can be made by reducing the exposure
time or by passive shielding. Passive shielding may cause an increased risk by increasing thedose equivalent from any generated secondary particles, projectile and target fragments(including neutrons). For shielding effectiveness, the use of a shielding material with a lowmean atomic mass is generally better.
(321) Information about radiation transport codes (see Chapter 5) is important and thestrengths and weaknesses of the codes should be investigated in detail via benchmarking
procedures against experimental data, including data obtained with advanced
anthropomorphic phantoms exposed at accelerators. The physics at the basis of the particle
transport and cross sectional data tables must also be improved to further develop the codes.
7.2

Area monitoring(322) Area monitors at well selected locations in the spacecraft can determine theenvironmental conditions and are appropriate for an immediate warning about changing
exposure conditions.
(323) Instruments are required to determine the radiation environment in terms of particle
type, fluence rate, energy, and direction distributions and, in some instances, dose quantities.
Dose quantities used to assess doses to astronauts and to monitor radiation at a number oflocations should give values of the dose rate. These data can be used to implement ALARA.
Area monitors at well selected locations in the spacecraft can be appropriate for immediate
warning about changing exposure conditions. This can be of importance before or during
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SPEs, electron belt enhancements, and EVA. Real-time calibration of instruments should be
explored.
(324) If appropriately designed and accurately calibrated instruments are used, it may bethat a quantity measured in fixed position in a spacecraft can, along with appropriate
occupancy data, provide the basis for an adequate assessment of doses to an astronaut or ofdoses to the local skin or the extremities. While in principle this procedure may be applicable
to astronauts in space, the large variation of the radiation field in intensity and composition ofradiation types inside a spacecraft, and its variation with time together with the flexibility of
the astronaut´s position, has the consequence that area monitoring is not sufficient tocompletely substitute individual monitoring, especially considering the high individual doses
to astronauts and the interest in providing a basis for individual risk estimates.
7.3

Individual monitoring(325) The assessment of organ and tissue absorbed doses, together with radiation quality
factors, of individual astronauts can be accomplished by calculations using anthropomorphic
phantoms or by measurements using personal dosemeters (see Chapter 6).
(326) One method of calculation of organ and tissue absorbed doses and radiation quality
factors does so directly for a standard male or female phantom for various locations in aspacecraft with appropriate shielding. The phantoms can be adjusted to approximate aparticular astronaut. The results are normalized using readings of area monitors and personal
dosemeters. Another method requires knowledge of particle fluence and applies conversion
coefficients from particle type, energy and direction distribution of fluence to organ andtissue absorbed doses and corresponding radiation quality factors for uniform irradiation ofan astronaut.
(327) Individual monitoring is mostly performed using personal dosemeters worn at thesurface of the body. The personal dosemeter serves as the dosemeter of record. A single
dosemeter system is, however, not sufficient to provide an assessment of the absorbed dose at
the surface of the body weighted by radiation quality. The broad range of different types ofparticle requires at minimum two detectors, one sensitive to low-LET radiation and the otherto high-LET radiation. Because of a possible anisotropy of the exposure in the spacecraft due
to variations of shielding properties, it may be useful to wear more than one dosemeter. Also
care needs to be taken regarding low-energy electrons and particles which are stopped in theskin and, therefore, contribute only marginally to organ doses other than the skin dose, but
may induce a large signal in an external dosemeter.
(328) The use of adequate active personal radiation detectors would enable improved
characterization (input energy, nuclear abundance, fluence rate, direction) of the radiation
field both on the body of the astronaut as well as in the environment. The measurement of
dose-rate can contribute directly to ALARA.
(329) The results of bio-marker measurements can be additionally used to estimate
individual radiation exposure. The determinations can be collaborative and provide all theexperimental radiation information and relative codes needed to achieve an efficient risk
assessment, minimizing the uncertainties in the final risk estimates.
7.4

Dose recording(330) Astronauts in space are exeptionally exposed and the assessment of their individual
doses should be part of the radiation protection programme for space flights. Astronauts
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should be informed of their doses and risk assessments as soon as possible. Their doses
should be regularly registered and a long term registry for all missions should be maintained.
(331) The dose record is the formal statement of the crew member’s exposure and should
be kept as a confidential medical record. The record should contain the history of the
exposure and all the calculation and experimental results, including all information on theparticle type energy and direction distributions of fluence; computer codes; conversion
coefficients and weighting factors; area monitor, personal dosemeter, and biomarker results
7.5

Consideration of uncertainties(332) There are large uncertainties in projecting cancer risks and the risks of other lateeffects from ionising radiation on Earth. Space radiation carries additional considerations,which further increase uncertainties. As radiation workers approach a significant fraction of
exposure limits, the calculations of uncertainty bounds is needed because exposures leading
to acceptable levels of risks may no longer be confidently avoided when the uncertainties are
considered.
(333) It is important to provide all the information needed to establish the uncertainties ofthe organ risk estimates. The overall uncertainty will be reduced by improvements inmodelling of radiation sources and the transport of the field through the spacecraft or habitat;
improved accuracy of radiation transport codes; improved accuracy of radiation monitoring;
better estimation of dose and dose-rate effectiveness factor; better determination of radiation
quality factors; better understanding of the statistics and dosimetry of epidemiological data.
(334) A full risk model may need to be developed using real time radiation readings, space
weather forecasts, and risk assessments. This can allow changes to the mission, with anassessment of uncertainties, whilst maintaining the total risk below predefined limits.
(335) Uncertainties in estimates of exposures and the relationship between exposure andrisk are a major concern for operational radiation protection in space due to the types ofradiation, which includes heavy ions and neutrons, and the higher exposure levels, which
may approach exposure and risk limits. Figure 7.1 illustrates schematically an operational
approach where an evaluation of uncertainties is included in the radiation protection approach(Schimmerling, 2010). Obviously, “acceptable“ levels of cumulative exposure depend on theuncertainty and hence reduction of uncertainties is seen to be an important task for mission
planning. Methods to estimate uncertainties in exposure and risks are described elsewhere(Cucinotta et al., 2011; NCRP 2006)

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Risk of exposure induced death

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Cumulative radiation exposure

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Fig. 7.1. Schematic view of risk management with ALARA and large uncertainties. The risk
distribution function versus cumulative radiation exposure with and without considering uncertainties(based on 95% confidence limit (CL)) is displaced. ALARA practices and action levels for an“acceptable” level of risk and permissible exposure limit (PEL) are also shown (Schimmerling, 2010).

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8.

CONCLUSIONS(336) Astronauts in space are living under extraordinarily different environmental
conditions than on Earth. The radiation environment in space needs specific attention andconsiderations regarding the exposure of astronauts and the limitation of such exposures to alevel where the health risks are comparable to other risks during space missions.
(337) The number of astronauts undergoing missions in space is very small compared to
the number of occupationally exposed persons on Earth. In long-term missions, however,doses to the astronauts are generally higher than those at other working places on Earth.
Hence a more individually based dose and risk assessment should be performed for
astronauts in space compared to persons on Earth, where these exposures are usually muchless than the limits defined for occupationally exposed persons.
(338) The following points are specifically mentioned:
 The primary radiation field in space is complex and includes electrons, protons,
particles and heavy ions up to very high energies. Additional secondary radiation(e.g. -radiation, muons, neutrons and pions) is produced by interactions in thematerials of a spacecraft, its equipment, and in the astronauts.
 The physics at the basis of the particle transport and cross sectional data tables must
be improved to further develop the computational methods. There is a lack ofexperimental cross-section data for light fragments and neutrons. Codes need to be
improved to treat all primary and secondary cascades including photons, protons, lightions, heavy ions, mesons and electromagnetic cascades. The nuclear interaction
database needs to be updated, especially for neutrons and light ions.
 The simple concept of considering the differences in radiobiological effectiveness byradiation weighting factors, wR, e.g. a constant radiation weighting factor of 20 for all
heavy ions of all energies, is not appropriate for dosimetry in space and the quality
factor (Q) is applied for the definition of the quantity dose equivalent in an organ or
tissue of the human body.
 The basis for risk assessments for the astronauts are the dose equivalents in organs
and tissues of adult males and females, HT,QM and HT,QF, which are based on mean
absorbed doses, DT, and mean quality factors in the corresponding organs or tissues,
QT.
 Conversion coefficients which relate particle fluence to mean absorbed doses inorgans and tissues of the human body and corresponding mean quality factors for all
types of radiation present in space, are an important data base for the assessment of
the exposure of astronauts. For the estimation of radiation risks of astronauts based onmean absorbed doses in the body, an assessment of the uncertainty of DT and QT
would be very useful.
 The concept of operational dose quantities for area monitoring of external exposureand an assessment of effective dose is not applicable because many different types ofparticles are involved with very high energies. Instead the measurement anddetermination of particle fluence and its distribution in energy and direction is more
important and provides a basis for an assessment of doses.
 A broad range of instrumentation has been specifically designed for fluence and dose
measurements in space. Obviously a single instrument is not sufficient for adetermination of all particle fluences and their energy distributions and for an

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assessment of organ doses in the human body. Particle spectrometers, individual
dosemeters and specific instruments measuring the low-penetrating radiation on the
body of an astronaut are needed.
 While passive individual dosemeters are generally appropriate to measure mission
doses integrated over the flight time, active detector systems allow the measurementof fluctuations in the exposure and also the inclusion of warning capabilities, e.g. incases of a large SPE.
 The use of biomarkers of health effects is an attractive supplement to physicaldosimetry. Biomarkers from blood samples from astronauts can be used to assess
individual mission doses. In addition, biomarkers may serve for an individual risk
assessment or an indication for the presence of a disease. Biodosimetry is routinely
performed on the small population of astronauts involved in International Space
Station (ISS) missions, and would likely be used in future space missions. To be
useful as a biodosimetry method, the radiation quality dependence of the response of
the specific assay need to be known.
 The exposure of astronauts in space is a special case of environmental exposure quite
different from that on Earth. In space missions, especially in long-term interplanetary
missions, their exposure will be higher than the annual limits recommended for
exposure of workers on Earth. Although astronauts are exposed to ionizing radiation
during their occupational activities they are usually not classified as being
occupationally exposed in the sense of the ICRP system for radiation protection. Thus,
for a specific mission planned, reference levels for risks or doses may be selected at
appropriate levels and no dose limits may be applied for a given mission.

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REFERENCES:
Azimi-Garakani, D., Wernli, C., 1991. Rsponse and background study of various PADC materials.
Int. J. Radiat. Appl. Instr. Part D. Nucl. Tracks and Radiat. Meas. 19 (1-4)445-448
Agosteo, S., Colautti, P., Fazzi, A. et al., 2006. A solid state microdosimeter based on a monolithic
silicon telescope. Radiat. Prot. Dosim. 122, 382-386
Agostinelli, S., Allison, J., Amako, K. et al., 2003. GEANT4 – a simulation toolkit. Nucl. Instr. Meth.
in Phys. Res. A 506 (3), 250-303.
Allison J., Amako, K., Apostolakis, J. et al., 2006. Geant4 developments and applications. IEEE
Transactions on Nucl. Sc. 53 (1), 270-278.
Allkofer, O.C., 1975. Introduction to Cosmic Radiation, Buchreihe der Atomenergie, Bd. 10, Verlag
Karl Thiemig, München.
Alpen, E.L., Powers-Risius, P., Curtis, S.B., DeGuzman, R., 1993. Tumorigenic potential of high-Z,
high-LET charged particle radiations. Radiat. Res. 88, 132-143.
Alsmiller, R.G., JR., Irving, D.C., Kinney, W.E., Moran H.S., 1965. The Validity of the Straightahead
Approximation in Space Vehicle Shielding Design Studies. Second Symposium on Protection
Against Radiations in Space, Arthur Reetz, Jr., ed., NASA SP-71, 177-181.
Andersen et al., 2004. The FLUKA code for space applications: recent developments. Adv. SpaceRes. 34 (6), 1302-1310.
Apáthy, I., Deme, S., Fehér, I. et al., 2002. Dose measurements in space by the Hungarian Pille TLD
system. Radiat. Meas. 35, 381-391.
Apáthy, I., Akatov, Y.A., Arkhangelsky, V.V. et al., 2007. TL dose measurements on board theRussian segment of the ISS by the “Pille” system during Expedition-8, -9 and -10. Acta
Astronaut. 60, 322-328.
Atwell, W., 1994. Anatomical models for space radiation application- An Overview. Adv. Space Res.
415-422.
Badhwar G. D., 1997. The radiation environment in low earth orbit. Radiat. Res. 148, S3-S10.
Badhwar, G. D., Atwell, W., Badavi, F. F. et al., 2002. Space radiation absorbed dose distribution in ahuman phantom. Radiat. Res. 157, 76–91.
Badhwar, G.D., Cucinotta, F.A., 2000. A Comparison on Depth Dependence of Dose and Linear
Energy Transfer Spectra in Aluminum and Polyethylene. Radiat. Res. 153, 1-8.
Badhwar, G.D., Cucinotta, F.A., Braby, L.A., Konradi, A., 1994. Measurements on the Shuttle of the
LET spectra of galactic cosmic radiation and comparison with the radiation transport model.
Radiat. Res. 139, 344–351.
Badhwar, G.D, O’Neill, P.M., 1992. An Improved Model of GCR for Space Exploration Missions.
Nucl. Tracks Radiat. Meas. 20, 403-410.

128

DRAFT REPORT FOR CONSULTATION
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265

Badhwar, G.D., Patel, J. U., Cucinotta, F.A., Wilson, J.W., 1995. Measurements of Secondary
Particle Energy Spectrum in the Space Shuttle. Radiat. Meas. 24, 129-138.
Badhwar, G.D., Atwell, W., Reitz, G., Beaujean, R., Heinrich, W., 2002. Radiation measurements on
the Mir Orbital Station. Radiat. Meas. 35(5), 393-422.
Bahadori, A.A., Van Baalen, M., Shavers, M.R. et al., 2011. Effect of anatomical modeling on spaceradiation dose estimates: A comparison of doses for NASA phantoms and the 5th, 50th, and95th percentile male and female astronauts. Phys Med Biol 56, 1671-1694.
Bahadori, A.A., Van Baalen, M., Shavers, M.R. et al., 2012. Dosimetric impacts of microgravity: ananalysis of 5th, 50th, and 95th percentile male and female astronauts. Phys Med Biol. 57,
1047-1070.
Ballarini, F. et al., 2004. Nuclear models in FLUKA: present capabilities, open problems and future
improvements. SLAC-PUB-10813, SLAC, Stanford, USA.
Ballarini, F., Battistoni, G., Cerutti, F. et al. 2006. GCR and SPE organ doses in deep space withdifferent shielding: Monte Carlo simulations based on the FLUKA code coupled toanthropomorphic phantoms, Adv. Space Res. 37(9), 1791-1797.
Barkas, W.H., 1963. Nuclear Research Emulsions, Vol. I. Academic Press, New York.
Bartlett, D.T., Hager, L.G., Tanner, R.J., 2006. Results of measurements on shuttle missions to the ISS of
the neutron component of the radiation field. Adv. Space Res. 37, 1668–1671.
Battistoni, Muraro, S., Sala, P.R., Cerutti, F., Ferrari, A., Roesler, S., Fasso, A., Ranft, J., 2007. The
FLUKA code: Description and benchmarking" Proceedings of the Hadronic Shower Simulation
Workshop 2006 at Fermilab, M. Albrow, R. Raja eds., AIP Conference Proceeding 896, 31-49,(2007).
Beaujean, R., Kopp, J., Burmeister, S. et al., 2002. Dosimetry inside MIR station using a silicondetector telescope (DOSTEL), Radiat. Meas. 35, 433–438.
Benghin, V.V., 2008. On-board predicting algorithm of radiation exposure for the International Space
Station radiation monitoring system. J. Atmos. Sol.-Terr. Phys. 70, 675-679
Benton, E.R., Benton, E.V., 2001. Space radiation dosimetry in low-Earth orbit and beyond. Nucl.
Instr. Meth. B 184(1-2), 255-294.
Benton, E.V., Badhwar, G.D. (edt.), 2001. Prediction and measurements of secondary neutrons inspace. Radiat. Measurem. 33 (3), 227-392
Benton, E.R., Frank, A.L., Benton, E.V., 2000. TLD efficiency of 7LiF for doses deposited by highLET particles. Radiat. Measurem. 32 (3), 211-214
Berger, T., Hajek, M., Fugger, M. et al., 2006. Efficiency corrected dose verification withthermoluminescence dosemeters in heavy ion beams, Radiat. Prot. Dosim. 120, 361–364.
Bernabeu, J., Casanova, I., 2007. Moon surface radiation environment analysis for February 1956
solar event conditions. Adv. Space Res. 42 (12), 1906-1912.

129

DRAFT REPORT FOR CONSULTATION
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317

Bichsel, H., 1992. Stopping Power and Ranges of Fast Ions in Heavy Elements. Phys. Rev. A. 46,
5761-5773.
Bigbee, W.L., , W.,C. et al., 1998. Human in vivo somatic mutation measured at two loci: individuals
with stable elevated background erythrocyte glycophorin A (gpa) variant frequencies exhibit
normal T-lymphocyte hprt mutant frequencies. Mutation Research/ Fundamental and Molecular
Mechanisms of Mutagenesis 397 (2), 119-136.
Billings, M.P., Yucker, W.R., 1973. The computerized anatomical man (CAM) model. Summary
Final Report, MDC-G4655, McDonnell Douglas Company, Huntington Beach, CA.
Bilski, P. , Berger, T., Hajek, M., Reitz, G., (2011). Comparison of the response of various TLDs tocosmic radiation and ion beams: Current results of the HAMLET project. Radiat. Meas.,
doi:10.1016/j.radmeas.2011.03.023).
Blakely, W.F., Miller, A.C., Grace, M.B. et al., 2003. Radiation biodosimetry: Applications forspaceflight. Adv. Space Res. 31 (6), 1487-1493.
Boberg, P.R., Adams, J.H., Beaujean, N.L., et al., 1993. The mean charge state of solar energetic
oxygen at 10 MeV/nucleon. In: Proceedings of 23th ICRC, Vol. 3, 396-399.
Boschung, M., Fiechtner, A., Mayer, S., Wernli, C., 2008. Field calibration and comparison of
personal neutron dosemeter designs based on CR-39 for the use around high-energy accelerators.
Radiat. Meas. 43 (2-6), 1081-1084.
Brandt, W., Ritchie, H.R., 1974. Primary Processes in the Physical Stage. Physical Mechanisms in
Radiation Biology, R.D. Cooper, and R. Woods. Eds. Tech. Info. Center, US, Atomic Energy
Commission, 20-29.
Braun, H., Christl, M., Rahmstorf, S. et al., 2005. Possible solar origin of the 1470 year glacial
climate cycle demonstrated in a coupled model. Nature 438, 208-211.
Brechtmann, C., Heinrich, W., 1988. Fragmentation Cross Sections of 32S at 0.7, 1.2, and 200
GeV/nucleon. Z.Phys. A331, 463-472.
Brenner, D.J., Hall, E.J., 1992. Commentary 2 to Cox and Little: radiation-induced oncogenictransformation: the interplay between dose, dose protraction, and radiation quality. Adv.
Radiat. Biol. 16, 167-79.
Brooks, A.L., 1999. Biomarkers of exposure, sensitivity, and disease. Int. J. Radiat. Biol. 75, 14811503.
Caffrey, J.A., Hamby, D.M., 2011. A review of instruments and methods for dosimetry in space. Adv.
Space Res. 47 (4), 563-574.
Carlsson, J., Rosander, K., 1973. Effects of Multiple Scattering on Proton Beams in Radiotherapy.
Phys. Med. Biol. 18, 633-640.
Casolino, M., Altamura, F., Minori, M. et al., 2007. The Altcriss project on board the International
Space Station. Adv. Space Res. 40, 1746–1753.

130

DRAFT REPORT FOR CONSULTATION
4318

Charara, Y.M., Townsend, L.W., Gabriel, T.A. et al., 2008. HETC-HEDS Code Validation Using

4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367

Laboratory Beam Energy Loss Spectra Data. IEEE Trans. Nucl. Sci. 55 (6), 3164-3168
Chen, J., 2001. Physics of coronal mass ejections: a new paradigm of solar eruption. Space Science
Reviews 95, 165-190.
Clowdsley, M.S., Wilson, J.W., Kim, M.Y. et al., 2000. Neutron Environment on the Martian Surface.
Physica Medica XVII, 94-97.
Cornforth, M.N., 2001. Analyzing radiation-induced complex chromosome rearrangements bycombinatorial painting. Radiat. Res. 155, 643–659.
Compton, A.H., 1936. Recent developments in cosmic rays. Rev. Sci. Instrum. 7, 71-82
Cucinotta, F.A., Durante, M., 2006a. Cancer risk from exposure to galactic cosmic rays: implications
for space exploration by human beings. Lancet Oncol. 7(5) 431-5.
Cucinotta, F.A., Hu, S., Schwadron, N.A. et al., 2011b. Space radiation risk limits and Earth-MoonMars environmental models. Space Weather 8.
Cucinotta, F.A., Kim, M. Y., Chapell, L.J., 2011a. Space Radiation Cancer Risk Projections andUncertainties – 2010. NASA/TP-2011-216155
Cucinotta, F.A., Kim, M.Y., Schneider, S.I., and Hassler, D.M., 2007. Description of light ion
production cross sections and fluxes on the Mars surface using the QMSFRG model. Radiat.
Environ. Biophys, 46, 101-106.
Cucinotta, F.A., Kim, M.Y., Willingham, V., George. K.A., 2008. Physical and biological organ
dosimetry analysis for International Space Station Astronauts. Radiat. Res. 170 (1), 127–138.
Cucinotta, .F.A., Nikjoo, H., Goodhead, D.T., 2000. Model of the radial distribution of energy
imparted in nanometer volumes from HZE particles. Radiat Res. 153, 459-468.
Cucinotta, F.A. et al., 1997. Computational Procedures and Data-Base Development. In: NASA
Workshop on Shielding Strategies for Human Space Exploration. Eds.: Wilson J.W., Miller J.,
Konradi A., and Cucinotta F.A., NASA CP-3360.
Cucinotta, F.A., Schimmerling, W., Peterson, L.E. et al., 2001b. Space Radiation Cancer Risks andUncertainties for Mars Missions. Radiat. Res. 156, 682-688.
Cucinotta, F. A., Schimmerling, W., Wilson, J. W., Peterson, L. E., Badhwar, G. D., Saganti, P. B.,
Dicello, J. F., 2001a. Space radiation cancer risk projections for explorative missions: uncertainty
reduction and mitigation, NASA JSC Document (JSC-29295), NASA Washington DC.
Cucinotta, F.A., Townsend, L.W., Wilson, J.W. et al. 1995. Light Ion Component of the Galactic
Cosmic Rays: Nuclear Interactions and Transport Theory. Adv. Space Res. 17, 77-86.
Cucinotta, F.A., Wilson, J.W., Saganti, P. et al., 2002. Physics of the Isotopic Dependence of GCR
Fluence Behind Shielding. NASA TP-2003-210792.

131

DRAFT REPORT FOR CONSULTATION
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419

Cucinotta, F.A., Wilson, J.W., Shinn, J.L. et al., 1996. Effects of Target Fragmentation on Evaluationof LET Spectra From Space Radiations: Implications for Space Radiation Protection Studies.
Radiat. Meas. 26, 923-934.
Cucinotta, F.A., Wilson, J.W., Tripathi, R.K., Townsend, L.W., 1998. Microscopic Fragmentation
Model for Galactic Cosmic Ray Studies. Adv. in Space Res. 22, 533-537.
Cucinotta, F.A., Wilson, J.W., Williams, J.R. et al., 2000b. Analysis of Mir-18 results for physicaland biological dosimetry: Radiation shielding effectiveness in LEO. Radiat. Meas. 132, 181-191.
Cummings, J.R., Binns, W.R., Garrand, M.H. et al., 1990. Determination of the Cross Sections for the
Production of Fragments with Relativistic Nucleus-Nucleus Interactions I. Measurements. Phys.
Rev. C 42, 2508-2529.
Dachev, T., Atwell, W., Semones, E. Et al., 2006. B., Observations of the SAA radiation distribution
by Liulin-E094 instrument on ISS. Adv. Space Res. 37, 1672-1677.
Dachev, T., Tomov, B., Matviichuk, Y. et al., 2002. Calibration results obtained with Liulin-4 typedosimeters. Adv. Space Res. 30 (4), 917-925.
Dettmann, J., Reitz, G., Gianfiglio, G., 2007.MATROSHKA—The first ESA external payload on theInternational Space Station. Acta Astronaut. 60, 17-23.

Doke, T., Hayashi, T., Kikuchi, J. et al., 2001. Measurements of LET-distribution, dose equivalentand quality factor with the RRMD-III on the Space Shuttle Missions STS-84, -89 and -91. Radiat
Meas. 33(3), 373-87.
Durante, M., and Cucinotta, F.A., 2011. The physical basis for radiation protection in space. Rev.
Mod. Phys. 83, 1245–1281.
EC, 2009. Technical Recommendations for Monitoring Individuals Occupationally Exposed toExternal Radiation. Report Radiation Protection 160 of the European Radiation Dosimetry
Group, WG2. European Commission, Luxembourg.
Edwards, A.A. et al., 2005. Review of translocations detected by FISH for retrospective biologicaldosimetry applications. Radiat. Prot. Dosim. 113, 396-402.
Ersmark, T., Carlson, P., Daly, E. et al., 2007. Geant4 Monte Carlo simulations of the belt proton
radiation environment on board the International Space Station/Columbus. IEEE Trans. Nucl.
Sci. 54 (4), 1444-1453.
Evans, H.D.R., Bühler, P., Hajdas, W. et al., 2008. Results from the ESA SREM monitors andcomparison with existing radiation belt models. Adv. Space Res. 42, 1527-1537
Facius, R., Reitz, G., 2007. Space weather impacts on space radiation protection. In: Space Weather
Physics and Effects. Eds. Bothmer, V. and Daglis, I.A. Springer-Praxis Books in Environmental
Sciences, ISBN:3-540-23907-3
Failla, G., Henshaw, P., 1931. The relative biological effectiveness of x rays and gamma-rays.
Radiology 17, 1-43.

132

DRAFT REPORT FOR CONSULTATION
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470

Fano, U., 1963. Penetration of Protons, Alpha Particles, and Mesons. Annual Review of Nucler
Science, Vol. 13, Emilo Segre, ed. 1-66.
Fasso, A., Ferrari, A., Ranft, J., Sala, P.R., 2005. FLUKA: a multi-particle transport code. CERN2005-10, INFN/TC_05/11, SLAC-R-773
Fattibene, P., Callens, F., 2010. EPR dosimetry with tooth enamel: A review. Appl. Radiat. Isot.
68(11), 2033-116.
Fedorenko, B., Druzhinin, S., Yudaeva, L. et al., 2001. Cytogenetic studies of blood lymphocytes
from cosmonauts after long-term space flights on Mir station. Adv. Space Res. 27, 355-359
Fermi, E., 1940. Summer Lectures, University of Chicago.
Ferrari, A., 2007. Fragmentation in human tissue; from cancer terapy to space missions, paper
presented at NUFRA2007, 26 September 2007.
Ferrari, A., Ranft, J., Sala, P.R., 2001.The FLUKA radiation transport code and its use for space.
Proceedings of the 1st Intern. Workshop on Space Radiation Research and 11th Annual NASASpace Radiation Health Investigators' Workshop. Physica Medica 17 Suppl. 1, 1-295
Filius, R.W., 1965. Trapped protons of the inner radiation belt, Dissertation, Department of Physics
and Astronomy, University of Iowa.
Flesch, F., Hirzebruch S.E., Hüntrup, G. et al., 1999. Fragmentation cross section measurements ofiron projectiles using CR-39 plastic nuclear track detectors. Radiat. Meas. 31 (1-6), 533-536.
Flesch, F., Iancu, G., Heinrich, W., Yasuda, H., 2001. Projectile Fragmentation of Silicon Ions at 490
A MeV, Radiat. Meas. 34, 237 -240
Freden, S.C., Paulikas, G.A., 1964. Trapped protons at low altitudes in the South Atlantic magnetic
anomaly. J. Geophys. Res. 69, 1259-1269.
Fry, R.J.M., Powers-Risius, P., Alpen, E.L. et al., 1985. High LET radiation carcinogenesis. Radiat.
Res. 104, S188-S195.
Fuglesang, C., 2007. Using the human eye to image space radiation or the history and status of thelight flash phenomena. Nucl. Instrum. Meth. A 580, 861–865.
George, K., Cucinotta, F.A., 2007. The influence of shielding on the biological effectiveness ofaccelerated particles for the induction of chromosome damage. Adv. Space Res. 39, 1076–1081.
George, K., Durante, M., Wu, H., Willingham, V., Badhwar, G., Cucinotta, F.A., 2001. Chromosome
aberrations in the blood lymphocytes of astronauts after space flight. Radiat. Res. , 731-738.
George, K., Durante, M., Willingham, V. et al., 2003. Biological effectiveness of accelerated particles
for the induction of chromosome damage measured in metaphase and interphase human
lymphocytes. Radiat. Res. 160, 425-435
Goldhaber, A.S., 1974. Statistical models of fragmentation processes. Phys. Lett. 53B, 306-309.

133

DRAFT REPORT FOR CONSULTATION
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522

Goldhagen, P., Clem, J.M., J. W. Wilson, J.W., 2004. The energy spectrum of cosmic ray induced
neutrons measured on an airplane over a wide range of altitude and latitude. Radiat. Prot. Dosim.
110(4), 387-392.
Gong, J.K., Glomski, C.A., Guo, Y., 1999. A lifelong, wide-range radiation biodosimeter:
erythrocytes with transferrin receptors. Health Phys. 77(6), 713-718.
Goodhead, D.T., Munson, R.J., Thacker, J., Cox, R., 1980. Mutation and inactivation of cultured
mammalian cells exposed to beams of accelerated heavy ions. IV. Biophysical interpretation. Int
J Radiat Biol. 37, 135-167.
Gudowska, I., Sobolevsky, N., Andreo, P. et al., 2004 Ion beam transport in tissue-like media using
the Monte Carlo code SHIELD-HIT Phys. Med. Biol. 49 (10), 1935–1958
Gunther, W., Leugner, D., Becker, E. et al., 2002. Energy spectrum of 50-250 MeV/nucleon ironnuclei inside the MIR space craft. Radiat. Meas. 35 (5), 511-514
HAMLET, 2011. Human model MATROSHKA for radiation exposure determination of astronauts.
European Commission: Seventh Framework Programme (FP7) of the EU. www.fp7-hamlet.eu.
Hathaway, D.H., Wilson, R.M., Reichmann, E.J., 2002. Group sunspot numbers: Sunspot cycle
characteristics. Solar Physics 211, 357-370.
Heinbockel, J.H., Slaba, T.C., Blattnig, S.R. et al., 2011. Comparison of the transport codes
HZETRN, HETC and FLUKA for a solar particle event. Adv. Space Res. 47, 10791088.
Heinrich, W., Spill, A., 1979. Geomagnetic shielding of cosmic rays for different satellite orbits. J.
Geophys. Res. 84, 4401.
Henkner, K., Sobolevsky, N., Jäkel, O., Paganetti, H., 2004. Test of the nuclear interaction model in
SHIELD-HIT and comparison to energy distributions from GEANT4. Phys. Med. Biol. 54 (22),509-517
Hoff, J.L., Townsend, L.W., Zapp, E.N. 2004. Interplanetary crew doses and dose equivalents:
variations among different bone marrow and skin sites. Adv. Space Res. 34, 1347-1352.
Hufner, J., 1985. Heavy fragments produced in proton-nucleus and nucleus-nucleus collisions at
relativistic energies. Phys. Rep. 125, 129-185.
Hufner, J., Schafer, K., Schurmann, B., 1975. Abrasion-ablation in reactions between relativistic
heavy ions. Phys. Rev. C12, 1888-1898.
Hughes, H.G., Prael, R.E., Little, R.C., 1997. The LAHET/MCNP Code Merger. Los Alamos
National Laboratory, LA-UR-97-4891. X-Division Research Note XTM-RN(U)97-012.
IAEA, 2011. Cytogenetic dosimetry applications in preparedness for and response to radiation
emergencies. International Atomic Energy Agency (in press).
IAGA, 1992. The International Geomagnetic Reference Field (IGRF) 1991 Revision. International
Association of Geomagnetism and Aeronomy, Division V, WG 8, EOS Trans. AGU 73, 182.
ICRP/ICRU, 1963. Report of the RBE Committee of the ICRP and ICRU. Health Physics 9, 357.

134

DRAFT REPORT FOR CONSULTATION
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574

ICRP, 1977. Recommendations of the International Commission on Radiological Protection. ICRP
Publication 26. Ann. ICRP 1 (3).
ICRP, 1989. RBE for deterministic effects. ICRP Publication 58. Ann. ICRP 20 (4).
ICRP, 1991. 1990 Recommendations of the International Commission on Radiological Protection.
ICRP Publication 60. Ann. ICRP 21 (1-3).
ICRP, 1997. General Principles for the Radiation Protection of Workers. ICRP Publication 75. Ann.
ICRP 27 (1).
ICRP, 2003. Relative biological effectiveness (RBE), quality factor (Q) and radiation weighting
factor (wR). ICRP Publication 92. Ann. ICRP 33 (4).
ICRP, 2005. Low-dose Extrapolation of Radiation-related Cancer Risk. ICRP Publication 99. Ann.
ICRP 35 (4).
ICRP, 2007. The 2007 Recommendations of the International Commission on RadiologicalProtection. ICRP Publication 103. Ann. ICRP 37 (2-4).
ICRP, 2009. Adult reference computational phantoms, ICRP Publication 110, Annals of the ICRP 39(2).
ICRP, 2012. Conversion Coefficients for Radiological Protection Quantities for External Radiation
Exposures. ICRP Publication 116, Annals of the ICRP 40 (1).
ICRU, 1970. Linear Energy Transfer. ICRP Report 16. ICRU Publications: Bethesda, MD.
ICRU, 1978. Basic Aspects of High Energy Particle Interactions and Radiation Dosimetry. ICRU
Report 28. ICRU Publications: Bethesda, MD.
ICRU, 1985. Determination of Dose Equivalents Resulting from External Radiation Sources. ICRU
Report 39. ICRU Publications: Bethesda, MD.
ICRU, 1986. The quality factor in radiation protection. ICRU Report 40. ICRU Publications:
Bethesda, MD.
ICRU, 1988. Determination of Dose Equivalents from External Radiation Sources – Part 2. ICRU
Report 43. ICRU Publications: Bethesda, MD.
ICRU, 1992. Measurements of Dose Equivalents from External Photon and Electron Radiations.
ICRU Report 47. ICRU Publications: Bethesda, MD.
ICRU, 1993. Quantities and Units in Radiation Protection Dosimetry. ICRU Report 51. ICRU
Publications: Bethesda, MD.
ICRU, 2001. Determination of operational dose equivalent quantities for neutrons. ICRU Report 66.
Journal of ICRU 1 (3).
ICRU, 2010. Reference data for the validation of doses from cosmic radiation exposure of aircraftcrew. ICRU Report 84. Journal of ICRU 10 (2).

135

DRAFT REPORT FOR CONSULTATION
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628

ICRU, 2011. Fundamental Quantities and Units for Ionising Radiation (Revised). ICRU Report 85a.
Journal of ICRU 11 (1a).
ISO/IEC, 2005. Guide 98-3 Guide to the Expression of Uncertainty in Measurement (GUM).
International Organization for Standardization, Geneva.
ISO/IEC, 2007. Guide 99 International vocabulary of basic and general terms in metrology(VIM).
International Organization for Standardization, Geneva.
ISO/IEC, 2009. Guide 98-1 Uncertainty of Measurement – Part 1: Introduction to the Expression ofUncertainty in Measurement. International Organization for Standardization, Geneva.
Iwamoto, Y., Niita, K., Sakamoto, Y., Sato, T., Matsuda, N., 2007. Validation of the event generator
mode in the PHITS code and its application International Conference on Nuclear Data for
Science and Technology 2007 doi: 10.1051/ndata:07417
James, M.R., McKinney, G.W., Durkee, J.W. et al., 2009. MCMPX 2.7.X – New features being
developed. IEEE/NSS, Orlando, http://mcnpx.lanl.gov/
JCGM - Joint Committee for Guides in Metrology, 2008b. Evaluation of measurement data - Guide to
the expression of uncertainty in measurement. JCGM 100, ISO/IEC Guide 98-3.
JCGM - Joint Committee for Guides in Metrology, 2009. Evaluation of measurement data - An
introduction to the "Guide to the expression of uncertainty in measurement”. JCGM 104,
ISO/IEC Guide 98-1.
JCGM - Joint Committee for Guides in Metrology, 2008a. International vocabulary of metrology- Basic and general concepts and associated terms (VIM). JCGM 200, ISO/IEC Guide
99:2007
Jones, M. R., 2000. ACS WFC CCD Radiation test: The Radiation Environment. ACS Institutional
Science Report 00-09, Space Telescope Science Institue.
Katz, R., 1970. RBE, LET and z/βα. Health Phys. 18, 175-???.
Katz, R., Sharma, S.C., Homayoonfar, M., 1972. The structure of particle tracks. In: Attix, F.H.
Topics in Radiation Dosimetry. Supplement 1. 317-383. Academic Press, New York, London.
Kiefer, J., Schreiber, A., Gutermuth, F., Koch, S., Schmidt, P.,1999. Mutation induction by different
types of radiation at the Hprt locus. Mutation Research/Fundamental and Molecular Mechanismsof Mutagenesis 431 (2), 429-448.
Kiefer, J., Schmidt, P., Koch, S., 2001. Mutations in Mammalian Cells Induced by Heavy Charged
Particles: An Indicator for Risk Assessment in Space. Radiat. Res. 156, 607-611.
Kim, Y., Atwell, W., Tylka, A.J. et al., 2010a. Radiation dose assessments of solar particle events with
spectral representation at high energies for the improvement of radiation protection. 38th COSPAR
Scientific Assembly, paper number F24-0005-10.
Kim, Y., De Angelis, G., Cucinotta, F.A., 2011. Probalistic assessment of radiation risk of astronauts
in space missions. Acta Astronautica 68, 747-759.

136

DRAFT REPORT FOR CONSULTATION
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679

Kim, M.Y., Qualles, G.D., Slabba, T.C., Cucinotta, F.A., 2010b. Comparison of organ dose and dose
equivalent for human phantoms of CAM vs. MAX. Adv. Space Res. 45, 850-857.
Knoll, G.F., 2000. Radiation detection and measurement, 3rd edition. New York: John Wiley & Sons.
Knott, C.N. et al., 1996. Interactions of Relativistic Neon to Nickel Projectiles in Hydrogen,Elemental Production Cross Sections. Phys. Rev. C 53, 347-357.
Knott, C.N. et al., 1997. Interactions of Relativistic 36Ar and 40Ar Nuclei in Hydrogen: Isotopic
Production Cross Sections. Phys. Rev. C 56, 398-406.
Kolıskova, Z., Sihver, L., Ambrozova, I. et al., 2012. Simulations of absorbed dose on the phantom
surface of MATROSHKA-R experiment at the ISS. Adv. Space Res. 49, 230-236.
Konradi, A., Atwell, W., Badhwar, G. D., Cast, B. L., Hardy, K. A., 1992. Low Earth orbit radiationdose distribution in a phantom head. Nucl. Tracks Radiat. Meas. 20, 49–54.
Koshiishi, H., Matsumoto, H., Chishiki, A. et al., 2007. Evaluation of the neutron radiation
environment inside the International Space Station based on the Bonner Ball Neutron Detector
experiment. Radiat. Meas. 42, 1510–1520.
Lee, K., Flanders, J., Semones, E. Et al., 2007. Simultaneous observation of the radiation environment
inside and outside the ISS. Adv. Space Res. 40, 1558-1561.

Lenchek, A.M., Singer, S.F., 1962. Effects of the finite gyroradii of geomagnetically trapped
protons. J. Geophys. Res. 67, 4073-4075.
Lewis, B.J., Smith, M.B., Ing, H. et al., 2012. Review of bubble detector response characteristics andresults from space. Radiat Prot. Dosim. 150, 1-21
Lutz, G., 1999. Semiconductor radiation devices. Device Physics. Berlin: Springer Verlag.
Matsumoto, H., Goka, T., Koga, K. et al., 2001. Real-time measurement of low-energy-range neutron
spectra on board the space shuttle STS-89 (S/MM-8). Radiat. Meas. 33, 321-333.
Matthiä, 2012. DLR Cologne, personal communication (to be published).
Menzel, H.G., Paretzke, H.G., Booz, J. (eds), 1989. Implementation of dose equivalent meters basedon microdosimetric techniques in radiation protection. Radiat. Prot. Dosim.29 (1-2).
Mezentsev, A., Amundson, S.A., 2011. Global gene expression to low- or high-dose radiation in ahuman three-dimensional tissue model. Radiat. Res. 175(6), 677-688.
Miller, J., 1997. “Database development and laboratory validation“ in „Shielding Strategies for
Human Space Exploration, Wilson, J.W., Miller, J., Konradi, A., Cucinotta, F.A. eds. NASA CP3360, NASA Langley Research Center.
Mitaroff, A., Silari, M., 2002. The CERN-EU high-energy Reference Field (CERF) facility for
dosimetry at commercial flight altitudes and in space. Radiat. Prot. Dosim. 102, 7- 22.

137

DRAFT REPORT FOR CONSULTATION
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731

Narici, L., Belli, F., Bidoli, V. Et al., 2004. The ALTEA/ALTEINO projects: studying functional
effects of microgravity and cosmic radiation. Adv. Space Res. 33, 1352-1357.
NCRP, 1989. Guidanc on Radiation Received in Space Activities. NCRP Report No. 98. National
Council on Radiation Protection and Measurements. Bethesda, MD.
NCRP, 1990. The Relative Biological Effectiveness of Radiations of Different Quality. NCRP Report
No. 104. National Council on Radiation Protection and Measurements. Bethesda, MD.
NCRP, 1997. Acceptability of Risk from Radiation- Application to Human Space Flight. NCRP
Symposium Proceedings No. 3. National Council on Radiation Protection and Measurements.
Bethesda, MD.
NCRP, 2000. Radiation Protection Guidance for Activities in Low-Earth Orbit. NCRP Report No.
132. National Council on Radiation Protection and Measurements. Bethesda, MD.
NCRP, 2002. Operational Radiation Safety Program for Astronauts in Low-Earth Orbit: A Basic
Framework. NCRP Report No. 142. National Council on Radiation Protection andMeasurements. Bethesda, MD.
NCRP, 2006. Information Needed to Make Radiation Protection Recommendations for Space
Missions Beyond Low-Earth Orbit. NCRP Report No. 153. National Council on Radiation
Protection and Measurements, Bethesda, MD.
Niita, K., Iwamoto, Y., Sato, T., Iwase, H., Matsuda, N., Sakamoto, Y., Nakashima, H., 2007. A newtreatment of radiation behaviour beyond one-body observables International Conference on
Nuclear Data for Science and Technology 2007 doi: 10.1051/ndata:07398
Niita, K., Matsuda, N., Iwamoto, Y. et al., 2010. PHITS: Particle and Heavy Ion Transport code
System, Version 2.23. JAEA-Data/Code 2010-022.
Nikjoo, H., Uehara, S., Pinsky, L., Cucinotta, F.A., 2007. Modelling and calculations of the responseof tissue equivalent proportional counter to charged particles. Radiat. Prot. Dosim. 126, 512-518
NMDB, 2011. Real time database for high resolution monitor measurements. Neutron Monitor Data
Base. EU 7th research programme, http://www.nmdb.eu/?q=node/138
Nymnik, R.A., 1999. The problems of cosmic ray particle simulation for the near-Erth orbital andinterplanetary flight conditions. Rad. Measurements 30, 669-677.
Obe, G., Facius, R., Reitz, G. et al., 199. Manned missions to Mars and chromosome damage. Int. J.
Radiat. Biol. 75 (4), 429-433.
O'Sullivan, D., Zhou, D., Heinrich, W. et al., 1999. Cosmic rays and dosimetry at aviation altitudes.
Radiat. Meas. 31 (1-6), 579-584.
Otto, Th., 2010. Response of the DIS-1 personal dosimeter to neutrons, protons and other hadrons.
Radiat. Meas. 45, 1564-1567.
Payne, M.G., 1969. Energy straggling of heavy charged particles in thick absorbers. Phys Rev. 185,
611.

138

DRAFT REPORT FOR CONSULTATION
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783

Pellicioni, M., 1998. Radiation weighting factors and high energy radiation. Radiat. Prot. Dosim. 80,
371-378.
Pellicioni, M., 2009. (Private information).
Pelowitz, D.B., 2008. MCNPX User's Manual, Version 2.6.0. LA-CP-07-1473 (Los Alamos: New
Mexico)Plante, I., Cucinotta, F.A., 2008. Ionization and excitation cross sections for the interaction of HZEparticles in liquid water and application to Monte-Carlo simulation of radiation tracks. New J.
Phys. 10, 125020 doi: 10.1088/1367-2630/10/12/125020.
Posner, A.; Hassler, D. M.; McComas, D. J., 2005. A high energy telescope for the solar orbiter Adv.
Space Res. 36 (8), 1426-1431.
Prosser, J.S., Moquet,J.E., Lloyd, D.C., Edwards, A.A., 1988. Radiation induction of micronuclei inhuman lymphocytes. Mut.Res. Fundam. Molecular Mechan. of Mutag. 199(1) 37-45.
Reedy R. C., 1996. Constraints on solar particle events from comparisons of recent events andmillion-year averages. In: Solar Drivers of Interplanetary and Terrestrial Disturbances.
(Balasubramaniam K S, Kiel S. L, Smartt R N, Eds.) p. 429-436, ASP Conf. Ser. Vol.95,
Astronomical Society of the Pacific.
Reitz, G., Beaujean, R., Benton, E. et. al., 2005. Space radiation measurements on_board ISS – The
DOSMAP experiment. Radiat. Prot. Dosim. 116, 374 – 379.
Reitz, G., Berger, T., 2006. The MATROSHKA facility—Dose determination during an EVA. Radiat.
Prot. Dosim. 120 (1−4), 442−445.
Reitz, G., Berger, T., Bilski, P. et al., 2009. Astronaut’s organ doses inferred from measurements in ahuman phantom outside the International Space Station. Radiat. Res. 171, 225-235.
Reitz, G., 2012. Private communication
Sampsonidis, D., Papanastassiou, E., Zamani, M. et al., 1995. Fragmentation cross sections of 16O,
24
Mg, and 32S projectiles at 3.65 GeV/nucleon. Phys. Rev. 51(6), 3304-3308
Sato T., Endo A. and Niita K., 2010. Fluence-to-dose conversion coefficients for heavy ionscalculated using PHITS code and ICRP/ICRU Adult reference computational phantoms, Phys.
Med. Biol. 55(8), 2235-2246.
Sato T., Endo A. and Niita K., 2011. Dose estimation for astronauts using dose conversion
coefficients calculated by the PIHTS code and the ICRP/ICRU adult reference computationl
phantoms. Radiat. Environ. Biophys. 50, 115-123
Sato T., Endo A., Zankl M., Petoussi-Henss N., Niita K., 2009. Fluence-to-dose conversion
coefficients for neutrons and protons calculated using the PHITS code and ICRP/ICRU adultreference computational phantoms. Phys, Med. Biol. 54 (7), 1997-2014.
Sato, T., Endo, A., Niita, K., 2012. Comparison of mean quality factors proposed by ICRP, ICRU andNASA. COSPAR-2012 (to be published)

139

DRAFT REPORT FOR CONSULTATION
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835

Sato T., Niita K., Iwase H., Nakashima H., Yamaguchi Y., Sihver L., 2006. Applicability of particle
and heavy ion transport code PHITS to the shielding design of spacecrafts. Radiat. Meas. 41,
1142-1146
Sawyer, D. M., Vette, J.I., 1976. AP-8 Trapped Proton Environment for Solar Maximum and Solar
Minimum, NSSDC/WDC-A-R&S 76-06
Schimmerling, W., Wilson, J.W., Cucinotta, F.A. et al., 1999. Requirements for simulating spaceradiations with particle accelerators. In: Risk evaluation of cosmic- ray exposure in long-termmanned space mission (K. Fujitaka, H. Majima, K. Ando, H. Yasuda, and M. Susuki, Eds.).
Kodansha Scientific Ltd., Tokyo, 1-16.
Schimmerling, W., 2010. Accepting space radiation risks. Radiat. Env. Biophys. 49, 325-329.
Schlatt H., Zankl M. and Petoussi-Henss N. (2007), Organ dose conversion coefficients for voxel
models of the reference male and female from idealized photon exposures, Phys. Med. Bio. 53,
2123-2145.
Schmidt, E., Regulla, D., Kramer, H.M., 2002. The effect of 29 keV x-rays on the dose response ofchromosome aberrations in human lymphocytes. Radiat. Res. 158, 771-777.
Schmitz,Th., Waker, A.J., Kliauga, P., Zoetelief, H. (eds), 1995. Design, construction and use oftissue-equivalent proportional counters – EURADOS report. Radiat. Prot. Dosim. 61 (4).
Schoeftner, S., Blanco, R., de Silanes, I.L. et al., 2009. Telomere shortening relaxes X chromosome
inactivation and forces global transcriptome alterations. Proc. National. Acad. Sci. 106 (46),19393-19398
Semkova, J., Koleva, R., Shurshakov, V. et al., 2007. Status and calibration results of Liulin-5
charged particle telescope designed for radiation measurements in a human phantom onboard theInternational Space Station. Adv. Space Res. 40 (11), 1586-1592
Shinn, J.L., Cucinotta, F.A., Simonsen, L.C. et al., 1998. Validation of a comprehensive spaceradiation transport code. IEEE Trans. Nucl. Sci. 45(6), 2711-2719
Shurshakov, V.A., Akatov Y.A., Petrov, V.M. et al., 2004. MATROSHKA-R experiment onboard theISS: current status and preliminary results, 9th WRMISS meeting, Vienna, Sep.8-10.
Sihver L., Mancusi D., Niita K. et al., 2007. Recent developments and benchmarking of the PHITS
code. Adv. Space Res. 40, 1320-1331.
Sihver L., Mancusi, D., Niita, K. et al., 2008. Benchmarking of calculated projectile fragmentation
cross-sections using the 3-D, MC codes PHITS, FLUKA, HETC-HEDS, MCNPX_HI, andNUCFRG2. Acta Astronautica 63, 865-877.
Sihver, L., Sato, T., Gustafsson, K. et al. 2010a. An update about recent developments of the PHITS
code. Adv. Space Res. 45, 892-899
Sihver, L., Sato, T., Puchalska, M., Reitz, G., 2010b. Simulations of MATROSHKA experiments at
the international space station using PHITS. Radiat. Environ. Biophys. 49, 351-357.
Slaba, T.C., Qualls, G.D., Clowdsley, M.S. et al. 2010. Utilization of CAM, CAF, MAX, and FAX for140

DRAFT REPORT FOR CONSULTATION
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886

space radiation analyses using HZETRN, Adv. Space Res. 45(7), 866-883
Slaba, T.C., Kim, M.Y., 2009.

((Section 5.3, par (237) HZETRAN ))Smart, D.F., Shea, M.A., 2008. World grid of calculated cosmic ray vertical cutoff rigidities for
Epoch 2000.0. Proc. 30th International Cosmic Ray Conference: Caballero, R., D’Olivo, J.C.,
Medina-Tanco, G., Nellen, L., Sánchez, F.A., Valdés-Galicia, J.F. (eds.).Universidad Nacional
Autónoma de México, Mexico City, Mexico, Vol. 1, 737–740).
Snyder, W.S., Ford, M.R., Warner, G.G. et al., 1969. Estimates of absorbed fractions formonoenergetic photon sources uniformly distributed in various organs of a heterogeneous
phantom. MIRD Pamphlet No. 5. J. Nucl. Med. 10(Suppl. 3) 46–51.
Sobolevsky, N.M. 2003. The SHIELD transport code for Monte Carlo simulation of interaction of
hadrons and nuclei with complex extended targets. GSI
Spjeldvik, W.N., Rothwell, P.L., 1983. The Earth radiation belts, AFGL-TR-83-0240, Air Force
Geophysics Laboratory, Hanscom AFB, Massachusetts.
Spurny, F. , Dachev, T. S., 2003. Long-term monitoring of the onboard aircraft exposure level with aSi-diode based spectrometer. Adv. Space Res. 32(1), 53–58.
Taucher-Scholz, G., Kraft, G., 1999. Influence of radiation quality on the yield of DANN strand
breaks for SV40 DNA irradiated in solution. Radiat. Res. 151, 595-604.
Townsend, L.W., Cucinotta, F.A., 1996. Overview of nuclear fragmentation models and needs. Adv.
Space Res. 17(2), 59-68.
Townsend, L.W., Miller, T.M., Gabriel, T.A., 2002. Modifications to the HETC Radiation Transport
Code for Space Radiation Shielding Applications: A Status Report. 12th Biennial ANS
Radiation Protection and Shielding Division Topical Meeting, Sante Fe, NM.
Townsend, L.W., Miller, T.M., Gabriel, T.A., 2005. HETC radiation transport code development forcosmic ray shielding applications in space. Radiat. Prot. Dosim. 116, 135-139.
Townsend, L.W., Wilson, J.W., 1986a. Energy-Dependent Parameterizations of Heavy-Ion
Absorption Cross Sections. Radiat. Res. 106, 283-287.
Townsend, L.W., Wilson, J.W., Cucinotta, F.A., Norbury, J.W., 1986b. Comparison of Optical
Model Differences in Heavy Ion Fragmentation: Optical Versus Geometric. Phys. Rev. C 34,
1491-1495.
Tripathi, R.K., Wilson, J.W, Cucinotta, F.A., 2001. Medium Modified Two-Body Scattering
Amplitude from Proton-Nucleus Total Cross-Sections. Nucl. Instrum. Meth. Phys. Res B173,
391-396.
Trovati, S., Ballarini, F., Battistoni, G. et al., 2006. Human Exposure to Space Radiation: Role ofPrimary and Secondary Particles. Radiat Prot Dosim. 122, 362-366.
Tull, C.E., 1990. Relativistic Heavy Ion Fragmentation at HISS. LBL-29718. Univ. of Calif.

141

DRAFT REPORT FOR CONSULTATION
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937

Tucker, J.D., Tawn, E.J., Holdsworth, D. et al, 1997. Biological dosimetry of radiation workers at the
Sellafield nuclear facility. Radiat. Res. 148(3), 216-226
Tucker, J.D., 2008. Low-dose ionizing radiation and chromosome translocations: A review of the
major considerations for human biological dosimetry. Mutation Research/Reviews in Mutation
Research 659(3), 211-220
Tweed, J., Waker, S.A., Wilson, J.W. et al., 2005. Computational methods for the HZETRN code.
Adv. Space Res. 35(2), 194-201.
Uchihori, Y., Fujitaka, K., Yasuda, N., Benton, E., 2002. Intercomparison of Radiation Instruments
for Cosmic-ray with Heavy Ion Beams at NIRS (ICCHIBAN Project). J. of Radiat. Res. 43S(Space radiation research), S81-S85.
Vette, J. I., 1991. The AE-8 Trapped electron model environment, NSSDC/WDC-A-R&S 91-24.
Vral, A., Thierens, H., De Ridder, L., (1997). In vitro micronucleus-centromere assay to detect
radiation damage induced by low doses in human lymphocytes. Int. J. Radiat. Biol. 71, 61–68.
Waker, A.J., 1995. Principles of experimental microdosimetry.Radiat. Prot. Dosim. 61, 271-308.
Waters, L.S. ed., 2002. MCNPX User’s Manual, Version 2.3.0. Los Alamos National Laboratory
Report LA-UR-02-2607.
Webber, W.R., Southoul, A., Ferrando P. Gupta, M. 1990a. The Source Charge and Isotropic
Abundances of Cosmic Rays with Z=9-16: A Study Using New Fragmentation CrossSections.The Astrophys. J. 348, 611-620 (1990a).
Webber, W.R., Kish, J.C., Schrier, D.A., 1990b. Individual Isotopic Fragmentation Cross-Sections ofRelativistic Nuclei in Hydrogen, Helium and Carbon Targets. Phys. Rev. C41, 547.
Weil, M.M., Bedford, J.S., Bielefeldt-Ohmann, H. et al., 2009. Incidence of acute myeloid leukemia
and hepatocellular carcinoma in mice irradiated with 1 GeV/nucleon 56Fe ions. Radiat. Res. 172,
213-219.
WELMEC, 2008. Software Guide (Measuring Instruments Directive 2004/22/EC). WELMEC 7.2
Issue 4. WELMEC secretariat, Ljubljana, Slovenia.
Wernli, C., Fiechtner, A., Kahilainen, J., 1999. The Direct Ion Storage Dosemeter for the
Measurement of Photon, Beta and Neutron Dose Equivalents. Radiat. Prot. Dosim. 84(1-4), 331334
Wernli, C., Kahilainen, J., 2001. Direct ion storage dosimetry systems for photon, beta and neutronradiation with instant readout capabilities. Radiat. Prot. Dosim. 96(1-3), 255-259
Westfall, G.D., Wilson, L.W., Lindstrom, H.J. et al., 1979. Fragmentation of relativistic 56Fe. Phys.
Rev. C 19, 1309-1323.
Wiegel, B., Alevra, A.V., 2002. NEMUS - The PTB Neutron Multisphere Spectrometer: Bonner
Spheres and More. Nucl. Instrum. Meth. A 476, 36-41.

142

DRAFT REPORT FOR CONSULTATION
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989

Wilson, J.W., 1978. Environmental geophysics and SPS shielding. Lawrence Berkeley Laboratory
Report LBL-8581, pp 33-116.
Wilson, J.W., Tweed, J., Nealy, J.E. et al., 1994b. Galactic cosmic ray transport methods: Past,
present, and future.Adv. Space Res. 14, 841-852
Wilson, J.W., Tripathi, R.K., Qualls, G.D. et al., 2004. Space radiation transport method development.
Adv. Space Res. 34(6), 1319-1327
Wilson, et al., NUCFRG2, 1995b. An Evaluation of the Semiempirical Nuclear Fragmentation
Database. NASA TP 3533.
Wilson, J.W., Cucinotta, F.A., Miller, J. et al., 2001. Approaches and Issues Related to Shield
Material Design to Protect Astronauts from Space Radiation. Materials and Design 22, 541-554.
Wilson J. W., Cucinotta F. A., Shinn J. L., Simonson L. C., Dubey R. R., Jordan W. R., Jones T. D.,
Chang C. V., Kim M. Y., 1999. Shielding from solar particles events in space. Radiation
Measurements 30(3).
Wilson, J.W., Kim, M.Y., L.W., Schimmerling, W. et al., 1995a.
Protection. Health Physics 68, 50-58.

Issues in Space Radiation

Wilson, J.W., Nealy, J.E., Dachev, Ts.P. et al., 2007. Time serial analysis of the induced LEO
environment within the ISS 6A.. Adv. Space Res. 40, 1562-1570
Wilson, J.W., Nealy, J.E., Wood, J.S. et al., 1995c. Variations in astronaut radiation exposure due toanisotropic shield distribution. Health Phys. 69, 34-45.
Wilson, J.W., Shinn, J.L., Townsend, L.W., et al., 1994a. NUCFRG2: a semiempirical nuclear
fragmentation model. Nucl. Instrum. Meth. Phys. Res. B 94, 95-102.
Wilson, J.W., Townsend, L.W., Schimmerling, W. et al., 1991. Transport Methods and Interactionsfor Space Radiations. NASA RP 1257.
Wissmann, F., Langner, F., Roth, J., Schrewe, U., 2004. A mobile TEPC-based system to measure thecontributions to H*(10) at flight altitudes. Radiat. Prot. Dosim. 110, 347-349.
Wong, M., Schimmerling, W., Phillips, M.H. et al., 1990. The Multiple Scattering of Very Heavy
Charged Particles. Med. Phys. 17, 163-171.
Yang, T.C., George, K.A., Johnson, A.S. et al., 1997. Biodosimetry results from space flight Mir-18.
Radiat. Res. 148, 17-23.
Yasuda, H., Badhwar, G. D., Komiyama, T., Fujitaka, K., 2000. Effective dose equivalent on the
ninth shuttle–Mir mission (STS-91). Radiat. Res. 154, 705–713.
Yasuda, H., 2001. Responses of a direct ion storage dosimeter (DIS-1) to heavy charged particles.
Radiat. Res. 156 (6), 805-808.
Yasuda, N., Uchihori, Y., Benton, E.R. et al., 2006. The intercomparison of cosmic rays with heavy
ion beams at NIRS (ICCHIBAN) project, Radiat. Prot. Dosim. 120(1-4), 414-420.

143

DRAFT REPORT FOR CONSULTATION
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020

Zankl, M., Witmann, A., 2001. The adult male voxel model "Golem" segmented from whole-body CT
patient data, Radiation and Environmental Biophysics, 40(2), 153-162.
Zapp, E.N., Townsend, L.W., Cucinotta, F.A., 2002. Solar particle event organ doses and dose
equivalents for interplanetary crews: variations due to body size. Advances in Space Research,
30, 975-979.
Zeitlin, C., Fukumura, A., Heilbronn, L. et al., 2001. Fragmentation Cross Sections of 600
MeV/nucleon 20Ne on Elemental Targets. Phys. Rev. C 64, 24902.
Zeitlin, C., Heilbronn, L., Miller, J. et al., 1997. Heavy Fragment Production Cross Sections from1.05 GeV/nucleon 56Fe in C, Al, Cu, Pb, and CH2 Target. Phys. Rev. C 56, 388-3397.
Zeitlin, C., Heilbronn, L., Miller, J. et al., 2002. Charge-changing and fragment production crosssections of 28Si on elemental targets from 400 MeV/nucleon to 1200 MeV/nucleon, LBNL47655.
Zeitlin, C., Guetersloh, S.B., Heilbronn, L.H. et al., 2006. Measurements of materials shielding
properties with 1 GeV/u 56Fe. Nucl. Instr. Meth. Phys. Res. B 252, 308–318
Zhou, D., O’Sullivan, D., Semones, E., Heinrich, W., 2006. Radiation field of cosmic rays measured
in low earth orbit by CR39 detectors. Adv. Space Res. 37, 1764-1769.
Zhou, D., O’Sullivan, D., Semones E., Zapp, N., Johnson, S., Weyland, M., 2008. Radiation
dosimetry for high LET particles in low Earth orbit. Acta Astronautica 63 (7-10), 855-846
Ziegler, J.F., Biersack, J.P., Ziegler, M.D., 2008. SRIM - The Stopping and Range of Ions in Matter.
SRIM Co. ISBN 0-9654207-1-X.

144

DRAFT REPORT FOR CONSULTATION
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
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ANNEX
Conversion coefficients and mean quality factors for protons, neutrons, alpha particles
and heavy ions (2 < Z ≤ 28).
(1) Conversion coefficients for mean absorbed doses in organs and tissues for males andfemales based on the reference voxel phantoms (ICRP, 2009) are given for heavy ions(2<Z≤28) with energies from 10 MeV/u to 100 GeV/u. For the skin data are given for theenergy range from 1 MeV/u to 100 GeV/u. The exposure geometry is always isotropic (ISO)radiation incidence. The data were evaluated based on their calculated values using the
PHITS code (Sato et al., 2010).
(2) Based on the Q(L) function (ICRP, 1991), also mean quality factors for organs andtissues of the adult male and female reference phantom are given for the heavy ions andenergies mentioned above (Sato et al., 2010).
(3) In addition to the mean quality factors based on Q(L), data are presented for meanquality factors for organs and tissues of the adult male and female reference phantom basedon the Q-concept developed by Cucinotta et al. (Cucinotta et al., 2011a) (see 3.2.3). The data
were also evaluated based on their calculated values using the PHITS code (Sato et al.,2012).The quality factors are related to RBE for solid cancer, and those for leukaemia are
one-fourth of the corresponding data for solid cancer.
(4) Furthermore, conversion coefficients from ICRP Publication 116 (ICRP, 2012) for
isotropic (ISO) exposure and mean quality factors are given for protons, neutrons, and alphaparticles. The mean quality factors were evaluated based on their calculated values using the
PHITS code (Sato et al. 2009, 2010 and 2012). The energy range considered for theseparticles are the same as in ICRP Publication 116.

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